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HERBERT PECKHAM
with WADE ELLIS, JR.
and ED LODI
HANDS-ON BASIC
FOR THE ATARI® 400/800/1200XL
HANDS-ON BASIC
FOR THE ATARI® 400/800/1200XL
HERBERT PECKHAM
with WADE ELLIS, JR.
and ED LODI
Computer
A BOOK
McGRAW-HILL BOOK COMPANY
NEW YORK ST. LOUIS SAN FRANCISCO AUCKLAND
BOGOTA HAMBURG JOHANNESBURG LONDON MADRID
MEXICO MONTREAL NEW DELHI PANAMA PARIS
SAO PAULO SINGAPORE SIDNEY TOKYO TORONTO
HANDS-ON BASIC: For the ATARI® 400/800/1200XL
Copyright © 1983 by Computer Literacy. All rights reserved. Printed in the
United States of America. Except as permitted under the United States Copy¬
right Act of 1976, no part of this publication may be reproduced or distributed
in any form or by any means, or stored in a data base or retrieval system,
without the prior written permission of Computer Literacy.
1234567890HALHAL89876543
ISBN D-DT-DMTnM-l
ATARI is a registered trademark of Atari, Inc., a Warner Communications
Company. ATARI 400, ATARI 800, and ATARI 1200XL are registered
trademarks of Atari, Inc.
This book was set in Patina and Eras using the TEX composition system. The
editor was Charles E. Stewart; the production supervisor was Joe Campanella;
the book designer was Paul Quin; the cover designers were Oona Johnson
and Paul Quin. Halliday Lithograph Corporation was printer and binder.
Library of Congress Cataloging in Publication Data
Peckham, Herbert D.
Hands-on BASIC for the Atari 400/800/1200XL.
(A Computer literacy book)
Includes index.
1. Atari 400 (Computer)—Programming. 2. Atari 800
(Computer)—Programming. 3. Atari 1200XL (Computer) —
Programming. 4. Basic (Computer program language)
I. Ellis, Wade. II. Lodi, Ed. III. Title. IV. Series.
QA76.8. A8P43 1983 001.64'2 83-7973
ISBN 0-07-049194-1
CONTENTS
PREFACE I
Acknowledgments 2
INTRODUCTION 5
What Is BASIC? 5
Where Did BASIC Originate? 6
How To Use This Book 6
CHAPTER 1
GETTING ACQUAINTED WITH YOUR ATARI 400/800/1200XL
COMPUTER 9
1 — I OBJECTIVES 9
Connecting the Computer to Your TV Set and Turning it
On and Off 9
Using Direct Mode 9
Learning Screen Editing 10
1 —2 DISCOVERY EXERCISES 10
1—3 DISCUSSION 16
Connecting The Computer to Your TV Set and Turning it
On and Off 16
Using Direct Mode 16
Learning Screen Editing 18
1 —4 PRACTICETEST 19
vi Contents
CHAPTER 2
INTRODUCTION TO BASIC 21
2- 1 OBJECTIVES 21
Correcting Mistakes 21
Learning the Requirements for BASIC Programs 21
Telling the Computer What to Do 21
Entering and Controlling Programs 21
Using Variable Names in BASIC 22
2 — 2 DISCOVERY EXERCISES 22
2 — 3 DISCUSSION 30
Correcting Mistakes 30
Learning the Requirements for BASIC Programs 30
Telling the Computer What to Do 31
Entering and Controlling Programs 32
Using Variable Names in BASIC 33
2 — 4 PRACTICE TEST 35
CHAPTER 3
GRAPHICS 39
3— 1 OBJECTIVES 39
Using Text and Graphics Modes 39
Drawing Lines 39
Creating and Positioning Shapes 39
Using Animation 39
Using Color 40
3 — 2 DISCOVERY EXERCISES 40
3 — 3 DISCUSSION 51
Using Text and Graphics Modes 51
Drawing Fbints and Lines 51
Creating and Positioning Shapes 52
Using Animation 53
Using Color 54
3-4 PRACTICETEST
55
Contents vii
CHAPTER 4
COMPUTER ARITHMETIC AND PROGRAM MANAGEMENT
57
4-1 OBJECTIVES 57
Doing Arithmetic on the Computer 57
Using Fbrentheses in Computations 57
Using E Notation for Numbers 57
Formatting a Diskette 58
Storing and Retrieving Programs 58
4 — 2 DISCOVERY EXERCISES 58
4 — 3 DISCUSSION 66
Doing Arithmetic on the Computer 66
Using F^rentheses in Computations 67
Using E Notation for Numbers 68
Formatting a Diskette 69
Storing and Retrieving Programs 70
4— 4 PRACTICE JEST 71
CHAPTER 5
INPUT AND OUTPUT 75
5— 1 OBJECTIVES 75
Getting Numbers into a BASIC program 75
Printing out Variables and Strings 75
Spacing the Printout 75
Using the REM Statement 75
Working with Program Examples 76
5 — 2 DISCOVERY EXERCISES 76
5 — 3 DISCUSSION 85
Getting Numbers into a BASIC Program 86
Printing out Variables and Strings 87
Spacing the Printout 88
Using the REM Statement
89
viii Contents
5—4 PROGRAM EXAMPLES 90
Example 1 - Unit Prices 90
Example 2 - Concerting Temperature 92
Example 3 - Sum and Product of Numbers 93
5-5 PROBLEMS 95
5- 6 PRACTICE TEST 100
CHAPTER 6
DECISIONS AND BRANCHING 103
6— 1 OBJECTIVES 103
Making Transfer Decisions in Programs 103
Working with Program Examples 103
Finding Errors in Programs 103
6 — 2 DISCOVERY EXERCISES 104
6 —3 DISCUSSION 112
Making Transfer Decisions in Programs 1 12
a. Unconditional Transfers 1 12
b. Conditional Transfers 1 13
6 — 4 PROGRAM EXAMPLES 1 15
Example 1 - Printout of Number Fbtterns 1 1 5
Example 2 - Automobile License Fees 1 16
Example 3 - Averaging Numbers 121
6 — 5 FINDING ERRORS IN PROGRAMS 123
6 — 6 PROBLEMS 124
6— 7 PRACTICE TEST 128
CHAPTER 7
LOOPING AND FUNCTIONS 131
7— 1 OBJECTIVES 131
Using Built-in Looping Statements 131
Using Built-in Functions 131
Working with Program Examples 131
Contents ix
7 — 2 DISCOVERY EXERCISES 132
7 — 3 DISCUSSION 140
Using Built-in Looping Statements 140
Using Built- in Functions 144
7- 4 PROGRAM EXAMPLES 147
Example 1 - Finding the Average of a Group of Numbers 147
Example 2 - Temperature Conversion Table 148
Example 3 - Exact Division 149
Example 4 - Depreciation Schedule 150
7 — 5 PROBLEMS 153
7 — 6 PRACTICE TEST 157
CHAPTER 8
WORKING WITH COLLECTIONS OF NUMBERS 161
8- 1 OBJECTIVES 161
Learning to Use Single—and Double—Subscripted
Variables 161
Saving Space for Arrays 161
Using FOR NEXT Loops to Handle Subscripted Variables 161
Working with Program Examples 161
8 — 2 DISCOVERY EXERCISES 162
Subscripts 162
8 — 3 DISCUSSION 170
Learning to Use Single— and Double— Subscripted
Variables 170
Saving Space for Arrays 1 72
Using FOR NEXT Loops to Handle Subscripted Variables 1 73
8 — 4 PROGRAM EXAMPLES 1 74
Example I - Examination Grades 1 74
Example 2 - Course Grades 1 77
Example 3 - Array Operations 180
8 — 5 PROBLEMS 182
8 — 6 PRACTICETEST 188
x Contents
CHAPTER 9
STRING VARIABLES 191
9— 1 OBJECTIVES 191
Handling String Input and Output 191
Using String Functions 191
Working with Program Examples 191
9- 2 DISCOVERY EXERCISES 192
9 — 3 DISCUSSION 201
Handling String Input and Output 201
Using String Functions 201
9 — 4 PROGRAM EXAMPLES 203
Example 1 - String Reversal 203
Example 2 - Word Count 204
Example 3 - Replacement Code 204
9 — 5 PROBLEMS 206
9 — 6 PRACTICE TEST 207
CHAPTER 10
SOUND AND SUBROUTINES 209
10— 1 OBJECTIVES 209
Creating Music 209
Exploring Subroutines 209
Working with Program Examples 209
10-2 DISCOVERY EXERCISES 209
10 — 3 DISCUSSION 216
Creating Music 216
Exploring Subroutines 21 7
10 — 4 PROGRAM EXAMPLES 219
Example 1 - Writing a Song 219
Example 2 - Rounding off Dollar Values to Cents
Example 3 - Carpet Estimating 222
Example 4 - Designing a House 227
220
Contents xi
10- 5 PROBLEMS 231
10 — 6 PRACTICETEST 233
CHAPTER 11
RANDOM NUMBERS AND SIMULATIONS 235
11- 1 OBJECTIVES 235
Generating Random Numbers 235
Designing Sets of Random Numbers 235
Working with Program Examples 235
11—2 DISCOVERY EXERCISES 236
Setting up the Random-Number Generator 236
11-3 DISCUSSION 240
Generating Random Numbers 240
Designing Sets of Random Numbers 241
11—4 PROGRAM EXAMPLES 242
Example 1 - Flipping Coins 242
Example 2 - Random Integers 243
Example 3 - Distribution of Random Numbers 244
Example 4 - Random Walk 245
Example 5 - Birthday fairs in a Crowd 246
11—5 PROBLEMS 247
11— 6 PRACTICE TEST 249
CHAPTER 12
FILES 251
12— 1 OBJECTIVES 251
Storing Information to a File 251
Retrieving Information from a File 251
Modifying Information Stored on Files 251
Working with Examples 251
12 — 2 DISCOVERY ACTIVITIES 251
12 — 3 DISCUSSION 256
Storing Information to a File 256
Retrieving Information from a File 258
xii Contents
12-4 PROGRAM EXAMPLES 259
Example 1 - Mail List Data Entry Program 259
Example 2 - Mailing Label Program 260
Example 3 - Selected Labels Program 261
Example 4 - Modifying the MAIL.DAT file 261
Example 5 - Menu-Driven Mailing Program 264
12-5 PROBLEMS 265
12 — 6 PRACTICE TEST 266
APPENDIX A
GLOSSARY 269
APPENDIX B
PRACTICE TEST SOLUTIOMS 273
APPENDIX C
SOLUTIONS TO ODD-NUMBERED PROBLEMS
283
INDEX
301
PREFACE
This book is a modification of BASIC: A Hands-on Method, which
introduces students to BASIC on a number of different timesharing
computers. The earlier book has been revised and modified to be
used specifically on the personal computer manufactured by Atari,
Inc. The thinking behind and justification for the original work
remain unchanged and bear repeating.
Most BASIC programming texts have two serious drawbacks.
First, almost all the texts presuppose a knowledge of mathematics
that most of our intended readers do not have. Second, most texts re¬
quire readers to spend little, if any, time on the computer. Typically,
students try to study programming like any other subject and do
not experiment with or execute programs on the computer. Our
experience indicates that people understand text material better and
more rapidly when it is preceded by a good deal of hands-on ex¬
perimentation.
Most textbooks are used in classrooms and certainly many
people learn programming in this traditional setting. However, per¬
sonal computers will soon be in such widespread use that many
people will learn programming outside the classroom. This text has
been designed for anyone, in or out of the classroom, who wants to
learn to program the ATARI 400, the ATARI 800, and the ATARI
1200XL computers.
This book is structured to make learning easy. Each chapter
begins with a statement of objectives. Then discovery exercises let
the student experiment with BASIC and see the language in action.
Once students acquire a feel for BASIC, they can profitably proceed
to a more traditional treatment of the concepts.
The text has twelve chapters and three appendices. Each
chapter is a module of instruction that should require about one
or two hours of computer work and perhaps one or two hours text
2 Hands-on BASIC
study. Reviews at the end of each chapter let students test their
mastery of the objectives. The book can be used in different ways: as
a self-study text, as the text for an open-entry, open-exit, self-paced
course, and in tandem with a traditional lecture course.
People at any level from junior high through graduate school
should be able to use this book to learn programming skills in BASIC
rapidly and effectively. The student needs no knowledge of mathe¬
matics past introductory algebra, and the algebra used is mainly for¬
mula evaluation. Students with more advanced mathematical skills
can apply them to independent work on the computer.
All students will need access to an ATARI 400/800/1200XL
computer with a BASIC language cartridge, at least one disk drive,
and a black-and-white or a color TV set. Although most of the
work in the book can be done without a disk drive, the lack of a
disk drive significantly limits the potential of the ATARI computer.
Two documents furnished with the ATARI 400/800/1200XL
computer and three documents furnished with the ATARI disk drive
are valuable to the student. The Operators Manual tells how
to connect the parts of an ATARI BASIC system. The ATARI
BASIC Reference Manual is a source of technical information. The
Disk Operating System II Reference Manual describes the use of
a disk drive with the ATARI 400/800/1200XL computer. Two
other manuals concerning the disk drive, the Oiuner's Guide and
An Introduction to the Disk Operating System , are also referenced.
Acknowledgments
I thank Wade Ellis, Jr. and Ed Lodi of the Computer Tutors of
San Jose, California for their assistance in writing this adaptation of
BASIC: A Hands-on Method . and for their typesetting and com¬
position of the book using the TpX composition system. Additional
thanks go to Atari, Inc. for their generous assistance.
Herbert D. Peckham
We would like to express our deep appreciation to several sources.
The staff of the Context project at Stanford University were, as al¬
ways, extremely helpful. Special thanks are due to Lincoln Ong who
helped us immensely with transfering files, Dikran Karagueuzian for
his efforts in getting the files to their final form, and Lisa Lodi for
checking most of the book.
Preface 3
Finally, we are deeply grateful to our wives, Jane and Rose
Marie, for their patience and understanding throughout the writing
and production of this book.
Wade Ellis, Jr.
Ed Lodi
INTRODUCTION
Computers play a part in most of our daily activities. Without com¬
puters, businesses of all sizes, educational institutions, and various
branches of government would be unable to handle the bewildering
quantity of information that characterizes our society. Although the
routine use of computers has become a significant part of everyday
activities only in recent years, the trend will surely continue as the
price of computers continues to drop. More and more people will
need to know how to use computers if they are to participate fully
in our society.
What Is BASIC?
You are about to embark on the study of the computer language
called BASIC. BASIC is a very specialized language that permits
communication between you and the computer. This language is
not complicated and is certainly much easier to learn than Spanish
or French. BASIC has a simple vocabulary of a few words, a gram¬
matical structure, and rules of use just like any other language. Your
main tasks will be to learn the vocabulary of BASIC, become familiar
with its rules of grammar, and begin to see how the language lets you
use the computer to do what you want. We have intentionally kept
the level of mathematics in this book simple. Don't be too concerned
if your mathematical skills are a bit rusty. As we proceed, you will
have an opportunity to brush up on elementary mathematics.
One effective way to learn is to observe details and characteris¬
tics while performing a task. We will use this "discovery" strategy.
You will begin each chapter with a session on the computer. After
following the directions and observing the computer’s response to
your instructions, you will begin to acquire a feel for BASIC. Then
you will study written material that summarizes what you have
learned.
6 Hands-on BASIC
Where Did BASIC Originate?
The original version of BASIC was designed and written at
Dartmouth College under the direction of Professors John G.
Kemeny and Thomas E. Kurtz. In September 1963 they began to
create a programming language written from the user's point of
view. Much of the actual programming on the project was done
by Dartmouth undergraduate students. The birthday of BASIC was
May 1, 1964.
The success of this pioneering effort at Dartmouth attracted
national attention, and other institutions became interested. The
rest is history. What started as a project at a single college is now
an established part of the computer industry. Today nearly every
time-sharing computer supports some version of BASIC.
The enhanced versions have increased the power and
capability of the language significantly. The most recent develop¬
ment is the adaptation of BASIC for use on small, inexpensive per¬
sonal computers. ATARI BASIC for the ATARI 400/800/1200XL
computer, the language presented in this book, is a powerful and
flexible enhanced version of BASIC.
How To Use This Book
Each chapter begins with a brief statement of the objectives. Study
these objectives carefully to get a clear picture of precisely where
you're going.
The next section of each chapter is the discovery exercises.
In that section you will record the computer output in the space
provided, when appropiate, and try to answer any questions you
are asked. These activities will lead you through the ideas involved
and let you see BASIC working. Try to think about what will
happen in the situations that are set up. Your relationship with
the computer should be an active one. Whether your answers are
correct is not important. The important thing is to think carefully
about the questions and to try to answer them. The time you spend
thinking about questions will save you time later on.
Following the discovery exercises is a complete discussion of
the objectives. Since you will have already seen the ideas and con¬
cepts in action on the computer, your study of this material will be
much easier and more profitable.
Introduction 7
Typical programs are included in each chapter. These are
discussed in detail to show how elements of programming are pulled
together to produce a BASIC program.
Beginning with Chapter 5, we give a set of problems at the end
of each chapter. You should work enough problems to satisfy your-
self that you can write programs at the appropriate level. Solutions
to the odd-numbered problems are in Appendix C.
Finally, each chapter has a practice test that lets you review
your understanding of the material and discover needs for further
study. The answers to the practice tests are contained in Appendix
B.
CHAPTER 1
GETTING ACQUAINTED
WITH YOUR
ATARI 400/800/1200XL
COMPUTER
Since the computer may seem a bit strange and complicated at first,
we will proceed slowly. After a few sessions, routine operations will
seem very natural and will cause you no trouble. Initially, though,
be prepared for a certain “confusion quotient." Don’t hesitate to
review previously studied material if necessary.
1-1 OBJECTIVES
In this chapter you will become familiar with the computer and start
learning how it operates. You will do no BASIC programming until
the next chapter. Learning how to operate the keyboard and how
to enter and modify information is easy, but it is fundamental to all
that follows.
Connecting the Computer to Your TV Set and Turning it On and Off
Your ATARI 400/800/1200XL computer can be connected directly
to a color or black-and-white TV set. To do this, you will need to
connect the TV switch box that comes with the computer.
Using Direct Mode
One of the easiest ways to use the computer is in the direct mode.
No programming is involved; the computer carries out instructions
as they are entered. In due time you will learn how to do much more.
For the present, however, simple operations in the direct mode are a
good introduction to using the computer.
10 Hands-on BASIC
Learning Screen Editing
The information entered into a computer is rarley mistake free. You
need to know how to edit— how to change or correct material that
has been entered. A thorough knowledge of editing will save you a
great deal of time later on.
1 -2 DISCOVERY EXERCISES
Before beginning work on the computer, we must establish several
important points. On a typewriter, the letter L is often used for the
numeral 1. On the computer, however, the numeral 1 is with the
other numeral keys along the top row of the keyboard. Similarly,
the letter O is sometimes used for the numeral 0 on a typewriter,
but on the computer the 0 is found on the top row of the keyboard.
■ Don't use the L for the l!
Don't use the Oh for the 0!
The standard appearance of characters typed on ATARI com¬
puters is white on a black background. There is a key that causes
characters typed to appear black on a white background instead. On
the ATARI 1200XL, this key is next to the BREAK key at the top
right hand side of the computer. On the ATARI 400/800 computers,
it is the key with the symbol JH next to the ,SHIFT key on the right
hand side of the keyboard. Pressing this key causes any characters
typed subsequently to appear in reverse video (background in white
and characters in black). Avoid pressing this key until you become
familar with using your ATARI computer. Reverse video can be
turned off by pressing this same key again.
You will need to know the following locations. On the ATARI
1200XL computer, the SWITCH BOX receptacle is at the rear of the
computer; the POWER IN receptacle is also at the rear; the POWER
ON/OFF switch is at the rear, left hand side; and the CHAN switch
is next to the POWER IN receptacle.
On the ATARI 400/800 computers, the POWER IN receptacle
is on the right hand side of the computer; the POWER ON/OFF
switch is also on the right hand side; and the CHAN switch is next
to the POWER ON/OFF switch.
1. Now you are ready to begin work. Connect the TV switch box
to your TV set and switch it to COMPUTER. Plug one end of the
power cord into the POWER IN receptacle, and the other end into
Getting Acquainted With Your ATARI 400/800/1200XL Computer 11
2 .
3.
a wall plug. Plug the cable found at the rear of the computer into
the TV switch box (on the ATARI 1200XL, this cable must first be
plugged into the SWITCH BOX receptacle).
Locate the
RETURN
key at the right hand side of the keyboard.
The BASIC language cartridge is installed by pressing it firmly into
the appropriate slot. On the ATARI 1200XL, the slot is located on
the left hand side of the computer. On the ATARI 400/800, the
slot is located beneath the cartridge door found immediately above
the keyboard. Be sure to close the door after inserting the BASIC
language cartridge. Turn on the TV set and switch to channel 2.
Now turn on the POWER ON/OFF switch. Be sure the CHAN
switch is set to 2. After a few moments, you will see
READY
4.
5.
displayed on the screen. If not, reseat the BASIC cartridge, double
check all the switch settings, and try again. The square H is called
a cursor. It will be displayed on the screen most of the time.
Locate the keys on the right-hand side of the keyboard that have the
following (as well as other) symbols on them: +, -, *, and /. Note
that these are obtained without use of the
SH/FTl key.
Now type
PRINT 1+4
Has anything happened?
L
Now press
RETURN!
and record what happened.
6. Now type
1+4
and press [RETURN] . What happened?
12 Hands-on BASIC
The question mark (?) is an alternate way to enter PR I NT in ATARI
BASIC.
7. Now you know how to make the computer do addition. Let's explore
this further. Type
PRINT 20+54.7
and press
RETURN
. What happened?
i_
8. Type
PRINT 2+4
and press
RETURN
Record the output below.
i_
9. Type
PRINT 12.--2
and press
RETURN
. What happened?
L
What arithmetic operation does the / call for?
Getting Acquainted With Your ATARI 400/800/1200XL Computer 13
10. If you make a typing error, you can m o ve the curs or, ■ , back to
the error by holding down the CTRL ( CONTROL on the ATARI
1200XL) key and pressing the key with the symbol <— on it. Each
time you press , the cursor will move one place to the left. When
you reach the error, make the correction, and return to where you
left off typing. To return, hold down the [CTRL key and press the key
with the sy mbol —► on it. Then continue typing. However, you need
only press [RETURN] after making the correction if the remainder of
the line is complete and correct. When you press the [RETURN] key,
the computer may give the message ERROR. If this happens, try to
see what the problem is and retype the line.
Type the incorrect line
PR I HU 1+4
and press RETURN . What happened?
Now type
PRING 1+4
and don't press |RETURN] . Instead, move the cursor to the G using
[CTRL] and <— and type T. Press [ rETURnI . What happened?
11. Your TV screen sh ould b e fairly full now. Press the [CLEAR] key,
holding down the [SHfFT[ key at the same time. What happened?
Pressing [CLEAR| clears the screen. If the screen is full and new lines
are entered, old lines will scroll off the top.
12. Type
PRINT 2*58
and press
. What happened?
14 Hands-on BASIC
What arithmetic operation is called for by the *?
13. Type
PRINT <2+35*4-1
you press
press
RETURN
RETURN
?
Press
RETURN
and record what happened.
L
14. Type
PRINT "<;
2 + 3 >*4-1"
and press
i
RETURN
. What happened?
What will happen if you type
PRINT "Bf
DOG 1 '
and press
RETURN
?
Try it and see if you were correct.
16. Let’s move on to a different topic. First, clear the scree n. If you have
forgotten how, look back at step 11. Type and press RETURN] .
QUIZ = 35
Then type
PRINT QUIZ
and press |RETURN| . What happened?
Getting Acquainted With Your ATARI 400/800/1200XL Computer 15
17. Take a few moments to examine the lines below.
LENGTH=10
WID T H=6
HE ILHT = 4
UOLUME=LENGTH*HIDTH*HEIGHT
PRINT VOLUME
What do you think will happen if you type in these lines?
Now type in the lines remembering to press
each line. What happened?
RETURN
at the end of
18. Study the lines below briefly.
LENGTH=12
WIDTH=9
SQYDS=<LENGTH $NID T H>/9
PRINT SQYDS,"SQYDS"
What will happen if you type in these lines?
L
Clear the screen and type in the lines, remembering to press
after each line. What happened?
ret urn I
19. This concludes the discovery material for this chapter. Turn off your
computer and TV set.
16 Hands-on BASIC
1-3 DISCUSSION
Connecting The Computer to Your TV Set and Turning it On and Off
See the Operators Manual for instructions on connecting your
ATARI computer to the TV set. Except for parts of Chapter 3 and
a few examples, a color TV set is not required.
The computer is simplicity itself to turn ON and OFF! As you
have already seen, this is done with the switch at the left side of
the computer (right hand side on the ATARI 400/800). Be sure the
BASIC language cartridge is inserted before turning on the computer.
The
READY
that appears on the screen indicates that you are in ATARI BASIC.
This procedure will be referred to as bringing up ATARI BASIC.
One important point: If things get away from you, if you lose
touch, or if the computer seems out of control, you have a way to
regain control. Simply press the RESET key (SYSTEM RESET key
on the ATARI 400/800). This should put you back where you were
before things seemed to go out of control. If that doesn't work, you
can also recover by turning the computer off and on again. If you
use this remedy, however, you will lose any programs or information
in memory. If neither of these remedies works, the BASIC cartridge
is probaby not seated properly in the slot. Reseat it and try again.
Using Direct Mode
In the discovery activities, you learned how to do simple arithmetic
operations using the computer like a simple calculator. This is also
known as the direct mode. As we shall see in the next chapter,
you can use BASIC to store statements and commands in a series
of numbered lines and then direct the computer to perform all the
statements at the same time. If, however, you type in the statements
without line numbers, the computer assumes you want a direct or
immediate answer and does what you asked it to do, if possible.
When you type in m aterial, nothing happens until you press
RETURN! . The [RETURN! key tells the computer you are through
typing a piece of information. In a few cases, the compute r respon ds
to a single keystroke and you do not have to press [RETURN .
However, such cases are the exception rather than the rule.
Getting Acquainted With Your ATARI 400/800/1200XL Computer 17
You have discovered that addition and subtraction are called
for by + and — , which probably wasn't much of a surprise!
Multiplication and division are indicated by * and /, respectively.
Parentheses can be used to group operations any way you wish. A
number of other clever operations are possible, but we will postpone
discussion of these to later chapters. If you type
PRINT 5Sc3.2 + 6.3
and press RETURN] , the computer will carry out the arithmetic and
print the result.
If you type
PRINT "ABCDEFG”
and press [RETURN] , the computer is instructed to print out the
collection of characters between the quotation marks— in this case
the letters ABCDEFG. Such a collection is called a “character string/'
an important concept that we will return to throughout the book.
The computer can keep track of a number of pieces of infor¬
mation in the direct mode. Thus, if you type
A = 2
B = 3
PRINT A+B
the computer will print 5 on the screen. There is a very important
point in connection with this concept. If you type
PRINT TAK
and press [RETURN , the computer will display 0. Since you gave
no value to TAX, the computer assigned the value 0 and printed it
out.
The computer is very relaxed about names for quantities used
either in the direct mode or in BASIC programs. You can use long
names like DEPTH or RATE as well as short names like D or R.
However, using long names can create problems. The long names
must be typed correctly each time they are used. Also, no spaces are
allowed in names. Certain words cannot be used for variable names,
because they are reserved for use by the computer. See Appendix A
of the ATARI BASIC Reference Manual for a list of reserved words.
18 Hands-on BASIC
This very brief introduction to the notion of variable names
suffices for our discussion of the direct mode. We will discuss the
concept more completely later in the book.
Recall from the discovery exercises that you can use ? as an
abbreviation for the PRINT statement. You can also use PR. as an
abbreviation for the PRINT statement. (Note: The period in PR.
is required.) Many of the BASIC statements you will learn have
abbreviations, but for clarity, we will use the full name in this book.
If you wish to abbreviate the names, you will find a list of most
of the statements and their abbreviations on the inside of the back
cover of the book. In addition, you will find a list of most of the
error messages and their meanings, on the inside of the flap of the
book cover.
Learning Screen Editing
The ATARI 400/800/1200XL computer has line editing commands
you can use to modify BASIC programs. However, errors can also
be corrected in the direct mode. We will limit our discussi on to the
two ways of making changes in a line before you press the [RETURN
key
First, you c an move the cursor to the left with the
D ELETE BACK SPACE] key ( DELETE BACK S| key on the ATARI
400/800 computer). As the cursor moves left, the character under
the cursor is erased. When the error is reached, you can make the
correction and resume typing from that point.
The second, and perhaps more useful me thod i s to move the
cursor to the left or right by holding down the [CTRL] key and then
pressing <— or —Characters do not get erased in this activity. You
make corrections by typing over the e rrors. If you need to delete
a character, you can hold down [CTRL| a nd move the cursor t o the
character you want to delete, then press [DELETE BACK SPACE] . You
can insert characters by moving the cursor to the character in front
of which you wish to insert a charac ter. Then continue to hold down
the [CTRL] key and press the [INSERT key. The computer will pro vide
a space for the character you want to insert,
is not used with
INSERT] when you use the |CTRL[
(Note: The
key.)
SHIFT! key
RETURN
When all the corrections have been made, you can press the
key regardless where the cursor is at t he time. If there are
many errors in a line, you may wish to press [RETURN] and retype
the line.
Getting Acquainted With Your ATARI 400/800/1200XL Computer 19
You can use these simple editing commands in the direct mode
to make changes or corrections. We will consider Further editing
features in the next chapter.
1 -4 PRACTICE TEST
Take the test below to discover how well you have learned the
objectives of Chapter 2. The answers to the practice test are given
in the appendix.
1. How do you let the computer know that you are through typing a
line?
2. If you lose control of the computer, how can you regain it?
3. What symbol indicates multiplication on the computer?
L
4. How do you clear the screen display?
i_
5. What operation does the symbol / indicate?
6. What will happen if you type
F'RINT 3*4'6
and then press
RETURN ?
L
20 Hands-on BASIC
7. What will happen if you type
PRINT 11 25 + 5 + 2"
and then press
RETURN ?
L
8. If you typed PRING 2+3*4 and noticed your spelling error before
you pressed |RETURN| , how could you correct the error?
CHAPTER 2
INTRODUCTION TO BASIC
Now you are ready to begin learning about programming in BASIC.
In this chapter you will learn to write and execute some simple
programs.
2-1 OBJECTIVES
Correcting Mistakes
If you're like everyone else, you'll make mistakes when entering in¬
formation into the computer. You will learn how to correct mistakes
even if you don't notice them until after you've typed several other
lines.
Learning the Requirements for BASiC Programs
All BASIC programs have characteristics in common. You will look
at some very simple programs to learn about these characteristics.
Telling the Computer What to Do
Commands tell the computer to do something to or with a BASIC
program. These action words control a program. You will look at
the LIST, RUN, and NEW commands.
Entering and Controlling Programs
This objective overlaps the one above. The main thing is to become
comfortable entering and controlling programs. All the programs
you will encounter initially are short and easy to handle.
22 Hands-on BASIC
Using Variable Names in BASIC
You must know how to name either numbers or strings of characters
in BASIC programs. Fortunately, the computer has very relaxed
rules about this.
2-2 DISCOVERY EXERCISES
In the discovery activities that follow, you will enter various pro¬
grams^ If you see a <RETURN)- in the instructions, p ress the
RETURN] key. Remember from Chapter 1 that pressing the [RETURN
1 .
key tells the computer that you are through typing. Now go on to
the activities below.
Turn on your computer and TV display and bring up ATARI BASIC.
(See step 3 of the discovery exercises in Chapter 1.)
2. Now type in
100 LET A= 1 <RETURN>
This is the first line of a BASIC program.
3. Now type in the balance of the program as listed below.
110 LET B=8 <RETURN>
120 LET C=A+B <RETURN>
130 PRINT C <RETURN>
140 END <RETURN>
4.
If you make mistakes typing the program, either retype the line or
correct it using the methods you learned in Chapter 1.
Clea r the s creen by pressing the key marked |CLEAR[ . Remember to
use
SHIFTl . What happened to the program you just typed in?
5. Fortunately, all is not lost. The computer remembers what y ou typed
in even though the screen is blank,
key. What happened?
Type LIST and press the [RETURN
Introduction To BASIC 23
6. On the TV display you should see the program you just entered. For
the time being, ignore the line numbers at the beginning of each line.
Just read the lines in the program and try to get a sense of what they
mean. If you tell the computer to carry out the instructions, what
do you think will happen?
Type RUN and press the |RETURN| key. What did happen?
7. Now type
110 LET B=5 <RETURN>
Clear the screen, type LIST, and then press the | RETURN| key. What
happened to line 110 in the program?
8. What do you think will happen if you tell the computer to execute
this program?
Type RUN, press the
Were you right?
RETURN!
key, and record what happened.
9. Now type
140 <RETURN>
Clear the screen and display the program using the LIST command.
What happened to line 140?
24 Hands-on BASIC
If you want to delete a line in a BASIC program, how do you do it?
L
10. Now run the program. What happened?
Does the computer need the END statement that used to be in line
140?
11. Experiment a bit more. Often you will want to clear a program from
the computer's memory. This is done with the NEW command.
Type NEW and press the
RETURN^ key. What happened?
Type LIST and press the [RETURN]
in memory. Is anything there?
key to see what the computer has
L
12. You have learned to clear out a program from memory, but now
you have no program left! To get the program back, you must enter
it again. Type in the program below.
109 LET A=1 < RETURN>
110 LET B = 8 <RETURN>
120 LET C=A+B <RETURN>
130 PRINT C <RETURN>
140 END <RETURN>
Check all the lines to make sure you entered them correctly. If you
need to change a line, retype it. If you have to retype lines, clear
LIST and pressing [RETURN
the screen by pressi ng [CLEAR] and redisplay the program by typing
Introduction To BASIC 25
13. Now type
125 LET D=B-h <RETURN>
135 PRINT D <RETURN>
Clear the screen and display the program. What has happened?
14. Take a few moments to study the program. What will happen if you
RUN the program?
Type run, press the
computer did.
RETURN] key, and record below what the
15. In the original program, the lines were numbered in intervals of ten
(e.g., 100, 110, 120, 130, and 140). Why are there "gaps" in line
numbers? (Hint: See step 13.)
i_
16. How do you insert lines in a BASIC program? (Hint: See steps 13
and 15.)
L
Clear th e program in memory by typing NEW and
[RETURN] key. Enter the program below.
nrpQ<;imr f-hp
100 INPUT WHITE <RETURN>
110 LET R E D = W H I T E + 2 <RETURN>
120 PRINT RED <RETURN>
130 GOTO 100 <RETURN>
140 END <RETURN>
26 Hands-on BASIC
18. This new program has several features that you have not seen before.
Study the program carefully and think about what will happen if
you run the program. What does the GOTO 100 in line 130 mean?
19. Run the program and record what the computer did.
Type the numeral 6 and press the
RETURN
key. What happened?
L
Type the numeral 10 and press the
return!
key. What happened?
20. What line in the program do you think is generating the question
mark?
Describe in your own words what the program is doing. If necessary,
experiment some more to make sure you are correct.
21. Now get out of the program. Press the |BREAK| key located at the
top right hand side of the computer (upper right hand side of the
keyboard on the ATARI 400/800). What happened?
22. Clear out the program in memory (see step 11). Type in the follow¬
ing program.
100 LET A=100 <RETURN>
110 PRINT A <RETURN>
120 LET A=A+1 <RETURN>
130 GOTO 110 <RETURN>
140 END <RETURN>
Introduction To BASIC 27
23. Run the program and record what happened.
When you get tired of watching the display, press
happened?
BREAK . What
24. Try it once more. Run the program and interrupt it after a few
numbers appear on the screen. How do you stop a BASIC program
running on the computer?
L
Now type CONT and press
i
[return
1 . What happened?
Stop the program by pressing
break! .
25. Clear the screen and display the program in memory. (See step 5.)
Type the line below. Note the absence of spaces in the line.
10 0 L EIA =1 <RETURN>
Clear the screen and list the program. What happened?
Now type the line below. Note the extra spaces.
1 0 0 L E T A = 1 <RETURN>
What happened?
List the program. Do there seem to be more statements in the
program now?
28 Hands-on BASIC
Clearly, some spaces are important in BASIC statements. Just note
the fact for now. We will return to this matter later.
26. Let's try a program with some new features. Cle ar the pro gram from
memory by typing NEW and then pressing the 1 RETURN] key. Type
in the program below.
100 PRINT "TYPE ft NUMBER" <RETURN>
110 INPUT FIRST <RETURN>
120 PRINT "ONE MORE TIME" <RETURN>
130 INPUT SECOND <RETURN>
140 LET SUM=FIRST+SECOND <RETURN>
150 PRINT "THEIR SUM IS" <RETURN>
160 PRINT SUM <RETURN>
170 END <RETURN>
27. Study the program for a few moments. Now run the program. What
happened?
Type the numeral 12, press the [RETURN] key, and record below
what the computer did.
28. Now type the numeral 13, press the [RETURN] key, and record below
what happened.
29. Now type in
LIST 120 <RETURN>
Move the cursor to the T in TIME by holding down CTRL] and using
the up arrow (on the same key with the minus sign) and the right
arrow. Replace TIME" with NUMBER PLEASE". Run the program
again.
30. This simple program illustrates that you can make BASIC programs
print out curt or courteous messages as well as numbers.
Introduction To BASIC 29
31. Now let's l ook at a different topic. Clear the screen. Type NEW and
press the [RETURN! key to clear the program from memory. Then
enter the following program.
100 DIM H$< 5 )
110 LET A = 1 <RETURN>
120 LET A$ = "HOUSE 11 <RETURN>
130 PRINT A <RETURN>
140 PRINT "A" <RETURN>
150 PRINT A$ <RETURN>
160 PRINT "AS” <RETURN>
170 END <RETURN>
32. This program contains something new. Look at the A$ in line 120.
Note that it is set equal to a word enclosed in quotation marks. The
balance of the program has to do with variations on printing out
A and A$. You will learn more about the DIM A$(5) statement in
later chapters. Run the program and record the output.
33. Study the output carefully and identify what the computer printed
in response to each of the PRINT statements. For the time being,
just make the comparison. Later you will examine the subject in
detail. Enter the following line:
165 PRINT B <RETURN>
34. Clear the screen and display the program with the LIST command.
Note that B is mentioned only in line 165 in the PRINT statement.
What do you think will happen if you run the program?
Now run the program and record what happened.
i_
35. As you saw in Chapter 1, even though the value of B was not defined
in the program, the computer assigned it a value of 0. This is an
important fact to remember when you write programs.
30 Hands-on BASIC
36. This concludes the discovery activities for this chapter. Turn off the
computer and go on to the next section.
2-3 DISCUSSION
Correcting Mistakes
Since most of us make mistakes while typing, we need to be able to
correct errors. Suppose you make a mistake typing a line. How you
corrected it depends upon whether you have pressed the RETURN
key yet. If you are on the line containi ng the error , you can move the
cursor left using both the CTRL key ( CONTROL key on the ATARI
1200XL) and the left arrow key and make corrections as you learned
in Chapt er 1. When all the corrections are made in a line, press the
[RETURN] key.
If you are not on the line that contains an error, you can
either retype the line to correct it or use LIST and the line number.
Then move to the error using the up arrow and left or right arrow
keys. You can make changes by typing over characters and using the
INSERT and DELETE keys, if necessary. Remember that you must
hold down the ICTRLj key whe n perfor ming any editing function. In
addition, you must press the RETURN) key while you are still on the
line for the corrections to be made. You should practice correcting
a line until you feel you have mastered correcting mistakes.
Learning the Requirements for BASIC Programs
You have inferred several important facts about BASIC programs.
As a point of reference, we will use the program you used earlier.
100 LET H=1
110 LET B=8
120 LET C=A+B
130 PRINT C
140 END
Each BASIC program consists of a group of lines called state¬
ments. Each statement must have a line number. The program above
has three BASIC statements: LET, PRINT, and END. The first two
statements will be treated fully in the next chapter. For the time
being, their function in this program is clear. The END statement is
not required with the ATARI computer. The computer will execute
Introduction To BASIC 31
the program with or without the END statement. However, it is a
good practice to use it, especially in long programs, so there will
be no confusion about where the program ends. Make it a rule to
use the END statement in all programs even though the computer
doesn't require it.
Generally the line numbers in a BASIC program are not con¬
secutive (e.g., 100, 101, 102, etc.) because you may want to insert
additional statements later if you discover errors or want to modify
the program. If there were no intervals between lines, you may have
to retype the entire program to make a change. "Gaps" in the line
numbers allow you to insert statements simply by typing in the new
statements with line numbers not already in the program.
As you saw in the discovery exercises, spaces are generally
important in BASIC program statements. The computer will let you
know whenever spaces are used incorrectly. If you write readable
statements, you should have no problems with spaces.
In BASIC the order in which you enter the lines makes no
difference. If you type
140 END
120 LET C = A+B
110 LET B = 8
130 PRINT C
100 LET A — 1
and display this new program, the computer will sort out the state¬
ments and display them in numerical order. In the same way, if you
were to execute the program as typed above, the computer would
sort the statements into the proper order before it executed them.
You can remove a BASIC statement from the program by
typing the line number and pressing the |RETURN| key. You can
modify statements by retyping lines or editing them as we have
shown. You can add new statements by using line numbers not
already in the program. Thus, you can add, remove, or change
BASIC statements as you wish. This ability to change programs
easily is a desirable characteristic of BASIC on the ATARI computer.
Telling the Computer What to Do
There is an important distinction between statements (lines in a
BASIC program) and commands. Commands tell the computer to
do something with a program. You have seen several of these in the
computer work, and we will briefly review the use of each.
32 Hands-on BASIC
When you enter a BASIC program, it goes into memory.
Quite often you need to see the program contained in memory,
perhaps because you want to see changes made in the program, or
perhaps because you simply need a copy of the program. In any case,
you use the LIST command. The wise programmer makes valuable
use of this command. If a program doesn't work as it should, your
first step should be to display the program in memory. You may
have the computer furnish a copy of the program stored in memory.
Use this copy to troubleshoot the program.
When you turn off the computer, the contents of memory are
cleared out automatically. When the computer is on, however, it
is possible to mix up programs. Suppose you are working on one
program and decide to go to another. If you don't clear the first
program out of memory, the second program will enter over the
first, and as a result parts of both programs may be in memory.
The way to avoid this is to clear out (or erase) a program with the
NEW command when you are through with it.
A BASIC program is simply a set of instructions on which the
computer acts. However, the computer needs to be told to start this
process. When the computer receives the RUN command, it goes
to the program statement with the lowest line number and carries
out the instructions. The computer then goes to the statement with
the next-to-lowest number and keeps on carrying out instructions in
numerical order, unless the program directs that a statement be done
out of order.
Entering and Controlling Programs
So far, when you have typed programs or comma nds, the
< RETURN > pr ompt ap peared to remind you to press the |RETURN]
key. Pressing [RETURN] should be a habit by now, so we will not
use the < RE TURN > p rompt in the future. From now on, remember
to press the |RETURNl key to let the computer know you are finished
typing a statement or command.
Sometimes you need to control a program that is running.
Certainly you would want to interrupt a program in a closed loop
because otherwise the program will run forever. You can break
into such a program by pressing the [BREAK] key. (Sometimes
you must press [BREAK twice.) The computer then interrupts
its execution of the program and displays STOPPED AT LINE
(whatever line was being processed when it was interrupted). The
Introduction To BASIC 33
comp uter resu mes program execution when you type CONT and
press
RETURN
You would also interrupt when the computer is in a n inpu t
loop waiting for a number to be typed in. Again, press |BREAK|
The computer will jump out of program execution and displays the
cursor ■.
Using Variable Names in BASIC
A common confusion for the beginner in BASIC is the distinction
between the name of the variable and the data stored under that
name. In the BASIC statement
100 LET A = 2
the A names a variable. Variable means that different values can
be assigned to A. Consequently, LET statements are often called
assignment statements. In this case the variable A is assigned the
value 2. What actually happens is that somewhere in the computer
memory there is a location named A, and the computer stores the
number 2 in that location. The fundamental distinction is between
the name of a location in memory and the contents of the memory
locations, much like the distinction between a post office box number
and the contents of that box. The box number does not change, but
the contents of the box may change at any time.
In ATARI BASIC, the use of LET in the assignment statement
is optional. In this book, we will always use LET in assignment
statements for the sake of consistency.
Consider the following statement.
138 LET C=A+B
This statement instructs the computer to get the numbers stored in
locations named A and B, add them together, and put the sum in
the storage location named C. The equal sign tells the computer to
evaluate what is on the right and assign it to the variable name on
the left. Now consider the BASIC statement
120 LET B=B+1
If we consider the statement above as an algebraic equation, we have
B= B + 1
34 Hands-on BASIC
If we subtract B from both sides of this equation, we have
0 — 1
which is very strange indeed! It is clear that in a BASIC statement
the = sign does not mean what it does in an algebraic equation.
Instead, the statement
120 LET B=B +1
instructs the computer to get the number stored in location B, add
1 to it, and put the result back in the storage location named B.
If you store a number in a location, anything that was stored
there before is lost. Consider the following statements:
100 LET A =1
110 LET A=2*3
Line 100 instructs the computer to set up a location called A and
put the number 1 in that location. Line 110 tells the computer to
multiply 2 by 3 and store the product in location A. The 1 stored
previously in location A is then lost.
To be precise, the variable A above is a “numeric" variable.
The reason for including numeric in the name is that there is another
type of variable called a “character string." You were introduced to
this concept briefly in the discovery activities.
It is easy to distinguish between numeric and character-string
variables. A, BOOK, M, and P would all identify numeric vari¬
ables and name numeric quantities. A$, BOOKS, MS, and PS all
name strings of characters. The $ symbol identifies the name as a
character-string variable. In the BASIC statement
100 LET B$= 11 BARN 11
BS names a location in memory in which the character string
“BARN” is stored. The quotation marks set off the string, but are
not part of it.
Recall that the ATARI computer has very relaxed rules for
variable names. It allows you to use “long" names for numeric vari¬
ables as well as character strings. You can use up to 110 characters
(including the $ character in the case of character strings) in long
names. The computer has a set of words that are reserved for com¬
mands and statements and cannot be used to name variables. See
Introduction To BASIC 35
the ATARI BASIC Reference Manual for the list of reserved words.
If you make a mistake and use one, however, the computer will often
let you know.
Let's go over the important points once more. A variable name
in BASIC identifies a storage location in memory that can contain a
number or character string. The contents of the storage location (the
value of the variable) may be changed, but the name of the location
cannot.
The LET (or assignment) statement evaluates what is on the
right side of the equal sign and assigns it to the storage location
named on the left side. Thus,
100 LET D = A+B + C
instructs the computer to evaluate the expression (A + B + C) using
the numbers stored in memory locations named A, B, and C. The
computer stores the result in the memory location named D. We will
return to the topic of character-string variables several times in this
book.
2-4 PRACTICE TEST
1. How do you signal the computer that you are through typing a line
or instruction?
L
2. Suppose that your computer is waiting for you to enter a number
in an INPUT statement of a program. You decide that you want
to jump the computer out of the program instead. How do you do
this?
i
3.
How do you interrupt a program that is running on your computer?
36 Hands-on BASIC
4. What is wrong with the following program?
100 LET A=1
110 LET B=3
120 LET C = B-h
PRINT C
130 END
5. What will happen if the program in question 4 were corrected and
run?
L
6. How long can variable names be?
7. How do you insert a line in a BASIC program?
L
8. How do you replace a line in a BASIC program?
9. How do you remove a line from a BASIC program?
L
10. How do you display the program in memory?
11. How do you erase the screen?
Introduction To BASIC 37
12. How do you command the computer to execute the program in
memory?
13. How do you erase a program in memory?
14. What is the difference between a numeric and a character-string
variable?
CHAPTER 3
GRAPHICS
3-1 OBJECTIVES
In this chapter we will discuss the graphics statements that are avail¬
able in the ATARI BASIC language.
Using Text and Graphics Modes
ATARI BASIC has three text modes and six graphics modes. You
will learn how to enter graphics modes to begin creating drawings
with your computer.
Drawing Lines
Straight lines are the basic component of many kinds of graphics.
You will learn to draw lines easily and quickly as a first step in
learning to make complex drawings on the display screen.
Creating and Positioning Shapes
You will learn to use your ability to draw lines to create shapes and
place them where you wish on the screen.
Using Animation
Moving figures on the screen make computing more interesting and
greatly increase the effectiveness of graphics displays. You will learn
how to make figures move about the screen.
40 Hands-on BASIC
Using Color
Colors make graphics more attractive. You will learn to draw with
colors and change background and border colors.
3-2 DISCOVERY EXERCISES
Turn on the computer and bring up ATARI BASIC. Remember to
press 1 RETURN] after you have typed a line. Type
GRAPHICS 8
What happened?
L
2. Now type
PLOT 160,80
What happened?
L
3. Type
COLOR 1
PLOT 160,80
What happened this time? (Look at the center of the screen.)
4. Now type
PLOT 310,5
PLOT 310,159
PLOT 5,159
Where do the points appear on the screen? (Look at the corners of
your screen. If your TV set is improperly aligned, some or all of
these points may not appear.)
Graphics 41
5. What should you type in to display or plot a point in the upper
left-hand corner of the screen?
i_
Try it and see if you were right.
6. Now type
GRAPHICS 8
Are the points still there?
i_
7. Type
10 PRINT "HELLO 11
20 PRINT "SAILOR"
30 END
and list the program. What happened?
i_
8. Now type
GRAPHICS 0
and again list the program. What happened this time?
i_
GRAPHICS 0 puts you back into standard text mode.
9. Type
GRAPHICS 8
PLOT 5,5
DRANTO 310,5
What happened?
42 Hands-on BASIC
10. Type
DRAWTO 310,159
DRAWTO 5,5
Draw the figure that appears on the screen.
Are all the lines solid?
Now type
DRAWTO 320,5
What happened?
L
Error 141 means the point (in this case 320,5) is off the screen. The
first number in the DRAWTO statement cannot be larger than 319.
Actually you may not be able to see the allowable corner points such
as 0,0 and 319,0 if your set is not adjusted very well.
11. Clear the graphics screen by typing
GRAPHICS 8
12. What statements would you enter to draw a box around the entire
graphics region? (See steps 3 and 4.)
i_
Enter the statements to see if you were correct.
Graphics 43
13. Let's draw a series of lines. Clear the graphics screen with the
GRAPHICS 8 statement. Type
PLOT 5,5
DRflHTO 50,5
DRAUTO 50,50
Draw the shape that appears on the screen.
14. Type
PLOT 5,5
DRhWTO 5,100
DRAWTO 100,100
What happened?
L
15. Clear the graphics screen. (See step 11.) Type
PLOT 10,10
DRAWTO 50,50
What happened?
44 Hands-on BASIC
Now type
PLOT 10+100.. 10+100
DRAWTO 50+100.. 50+100
Are the lines the same length?
Compare the two sets of statements that draw these lines.
16. Type
DRAWTO 200,150
Where did this line start?
17. Where will the line start that is drawn by
ORAWTO 10,10
Try it and see if you were right.
18. Clear the graphics screen. Type
COLOR 0
PLOT 0,0
DRAWTO 50,58
Was anything drawn on the screen?
Graphics 45
19. Type
COLOR 1
PLOT 0,0
DRAWTO 50,50
What happened?
20. Type
C 0 L 0 R 0
PLOT 0,0:DRHWTO 50,50
What color was used to draw this line?
COLOR 1 sets the drawing color to white. COLOR 0 sets the draw¬
ing color to the background color. Drawing a line with background
color over a white line has the effect of erasing the white line.
Note that you can put more than one statement on a line if
you separate them with a colon.
21. Clear the graphics screen and type
COLOR 1 : PLOT 10,10
DRAWTO 10, 30: DRAWT 0 30,30
DRHWTO 30 , 10 : DRAWTO 10 , 1 0
What was drawn?
How long is the edge of the figure?
L
Where did the figure start?
46 Hands-on BASIC
22. Now let’s use programs to draw shapes. Type
GRAPHICS 0
and then type the following program.
10 GRAPHICS 8
20 LET A=0
38 LET B=0
40 PRINT "EDGE LENGTH
50 INPUT E
6 0 C 0 L O R 1
70 PLOT A / B : DRAW TO A + E.- B
88 DRAWTO A+E,B+E
90 DRAWTO A,B+E =DRAWTO A,B
10 0 G 0 T O 2 O
110 END
Study the program. Use the points in the PLOT and DRAWTO
statements in lines 70, 80, and 90 to fill in the blanks in the following
diagram. Connect the points with lines as indicated in program lines
70, 80, and 90.
A,B A + E,B
,B + E A + E,
L
Run the program. Input 20, 40, 70, 100 and 150 at the question
mark prompts. What is the starting point for each figure?
Jump the program out of the input loop ( [BREAK
Graphics 47
23. Enter text mode by typing
GRAPHICS 0
Change lines 20 and 30 as follows.
28 PRINT "STARTING POINT ";
38 INPUT A,B
Display the program. Run the program. Enter 20,70 for the starting
point and 70 for the edge. What happened?
Now enter 100, 150 for the starting point and 70 for the edge. What
happened?
Avoid illegal quantities in DRAWTO statements if you wish the
program to continue executing. When you plot a point, the largest
first number you can use is 319, and the largest second number is
191.
24. Now that you are able to draw shapes by using the DRAWTO
statement, let's make the box move on the screen. Enter text mode
(see step 23) and display the program. Add lines 55, 56 and change
line 100 as follows:
55 LET h=A+1
56 LET B=B +1
i00 G0TO 55
Display the program. Check it against the complete program below.
10
20
30
40
50
55
GRAPHICS 8
PRINT "STARTING POINT
INPUT A,B
PRINT "EDGE LENGTH
INPUT E
LET A=A+1
H .
48 Hands-on BASIC
56 LET E: = B +1
60 COLOR 1
70 PLOT A/B : DRAWTQ A+E,B
80 DRAWTO A+E,B+E
30 DRAWTO A,B+E : DRAWTO A,B
100 GOTO 55
110 END
Run the program. Enter a starting point of 0,0 and an edge length
of 20. What happened?
Are you in text mode now?
L
Enter text mode (see step 23) and change lines 55 and 56 as follows.
55 LET A=A+3
56 LET B = B+2
Run the program entering 0,0 and 20 again at the input prompts.
Does the figure move faster?
Again, enter text mode and add the following lines to erase the box
right after it is drawn.
91 COLOR 0:PLOT A,B
92 DRAWTO A+E,B=DRAWTO A+E,B+E
33 DRAWTO A,B+E=DRAWTO A,B
COLOR 0 causes the DRAWTO statements in lines 92 and 93 to be
drawn in the background color. Run the program entering 0,0 for
the starting point and 20 for the edge. What happened?
Graphics 49
The box appears to move down the screen. In direct mode, type
PRINT A + E.-B + E
Which of these numbers was the illegal quantity?
L
If you are not using a color television set, go to step 31. Let's
investigate using color to draw lines. Enter text mode and clear the
memory and the screen. If you wish to check the color settings on
your display, type and run the following direct mode statements.
GRAPHICS 3
COLOR 1
P L 0 T 0 .■ 0
DR A WTO 20.-0
COLOR 2
PLOT 0,2
DRAWTO 20,2
C 0 L 0 R 3
PLOT 0,4
DRAWTO 20,4
GRAPHICS 3 puts the screen into low resolution graphics, in which
there are four colors available for drawing lines. These statements
will display three horizontal bars whose colors are orange, light
green, and dark blue, respectively.
Now type in the following direct mode statements, noting the
display as you do.
COLOR 0
PLOT 0,2
DRAWTO 20,2
COLOR 0 is black, the same as the backround.
50 Hands-on BASIC
27. Let’s look again at high resolution graphics and color. Look at the
screen after typing each of the following direct mode statements:
GRAPHICS 8
SETCOLOR 2,2,4
SETCOLOR 2,4,4
SETCOLOR 2,6,4
SETCOLOR 2,8,4
Did the background colors change?
28. Now type in
SETCOLOR 2,2,4
SETCOLOR 2,2,6
SETCOLOR 2,2,8
Did the background color get brighter?
29. Now type in
SETCOLOR 4,4,4
What happened to the border color?
i_
30. Type in
SETCOLOR 4,6,4
SETCOLOR 4,8,4
Did the border color change?
Graphics 51
Chapters 7 and 8 will present program flow controls that will help
you avoid illegal quantity errors. For now, we have completed the
discovery exercises. Turn off the computer.
3-3 DISCUSSION
Using Text and Graphics Modes
In the discovery exercises you saw two screen modes, text mode
and graphics mode. Actually, your ATARI computer has three text
modes and six graphics modes. To choose a particular mode you
must know of the attributes of each mode and what task you wish to
perform. (See Chapter 9 of the ATARI BASIC Reference Manual for
more details.) We have used the standard text mode, GRAPHICS
0, in this chapter as well as in the previous ones. You enter the
standard text mode every time you turn on your computer and bring
up ATARI BASIC. It provides a screen of 24 lines of text and 40
columns.
To enter the high resolution graphics mode, use the
GRAPHICS 8 statement. The high resolution graphics mode
provides a display of 320 points across and 160 points down. There
is also a narrow band at the bottom of the screen for 4 text lines.
This combination is called a split screen. You can obtain a full
graphics screen (320 points by 192 points by using the statement
GRAPHICS 8+16 instead of GRAPHICS 8. Adding +16 to any of
the graphics statements will give you a full screen rather than a split
screen. A full screen allows you to plot more points at the bottom
of the screen.
To enter the low resolution graphics mode, use the
GRAPHICS 3 statement. This will provide 40 points by 20 points
with a split screen.
■ Use GRAPHICS 8 to enter high resolution graphics mode.
Use GRAPHICS 3 to enter low resolution graphics mode.
Drawing Points and Lines
The PLOT statement is used to draw points. For example,
P L 0 T 0 .* 0
plots a point in the upper left-hand corner of the screen in the current
52 Hands-on BASIC
color. The point may not be visible if your set is not properly
aligned. The statements
PLOT 0,8
DRAUTO 313,159
plot a point at 0,0 and then draw a diagonal line across the screen
in the current color. The statements
PLOT 160,80
DRAUTO 160,159
plot a point at 160,80 (the center of the screen) and then draw a
line down to the point 160,159. The graphics pen is positioned at
the last point it draws.
■ Use PLOT to draw points, DRAWTO to draw lines.
Creating and Positioning Shapes
As you saw in the discovery exercises, creating shapes is a simple
matter of drawing lines to produce the desired shape. For example.
GRAPHICS 8
COLOR 1
PLOT 0,40• DRAWTO 10,0■ DRAWTO 20,40
DRAWTO 10,40: PLOT 10,40= DRAWTO 10,50
draws a pine tree when entered in direct mode.
To position this pine tree near the point 160,80, you would
use the following statements:
GRAPHICS 8
COLOR 1
PLOT 160+0,80+40 : DRAWT0 160+10,80+0
DRAWTO 160+20.< 80+40 : DRAWT0 160+0,80 + 40
PLOT 160+1 0,80+40 : DRAWTO 160+ 1 0 .« 80 + 50
You can select a starting point A,B while the program is run¬
ning by using an INPUT statement in the program. You can position
the figure anywhere you desire on the screen. Take care that no point
Graphics 53
has a first number larger than 319 or a second number larger than
191.
As you saw in the discovery exercises as well as in these last
two examples, you can put multiple statements on a single line if
separate them with the colon.
Using Animation
You can make a shape appear to move about the screen by first
drawing it at a particular position in white (or color) and then
redrawing it in the background color in the same position. Then
repeat the first two steps using a slightly different starting position.
If you continue to move the starting positions, the shape will appear
to move along the path of the starting positions. For example, the
program
1 0 0
GRAPHICS 8
110
LET A=0
120
COLOR 1
130
PLOT A+20 40 ■
DRAWTO A+23,
25
140
DRAWTO A+40,40
DRAWTO A+2
0,4 0
150
PLOT A+3 0 .■ 4 0 :
DRAWTO A+30,
45
160
PLOT A +1 0 .. 45 :
DRAWTO A+50,
45
170
DRAWTO A+45,50
: DRAWTO A+l
5,50
130
DRAWTO A+10,45
1 30
C 0 L 0 R 0
2 0 0
PLOT A+20.-40 :
DRAWTO A + 23,
•~i C J
210
DRAWTO A+40,40
: DRAWTO A+2
0 , 4 0
220
PLOT A+30,40 =
DRAWTO A+30,
45
2 3 0
PLOT A+10,45'
DRAWTO A+50,
45
240
DRAWTO A+45,50
= DRAWTO A+l
5, 50
250
DRAWTO A+10,45
260
LET A=A+15
270
GOTO 120
2 3 0
END
will cause a
sailboat to move across the top of the screen. You might
try this program on your computer. Notice that the value of the
variable A (which is changed in line 260) sets the starting point. As
the starting point changes, the position of the figure also changes.
54 Hands-on BASIC
Using Color
In high resolution graphics, lines can be drawn in one of two colors.
COLOR 1 causes a line to be drawn in what might be called white
(changing the background color causes variations in the color of the
line). COLOR 0 causes a line to be drawn in the background color.
In low resolution graphics, there are four colors available
for drawing lines. COLOR 1 draws lines in orange, COLOR 2
draws lines in light green, COLOR 3 draws lines in dark blue, and
COLOR 0 draws lines in the background color. Again, changes in
background color will change the color of the lines.
As you saw in the discovery exercises, the SETCOLOR state¬
ment can change the color and brilliance of the background and
border colors. For example, the statement SETCOLOR 2,4,6 will
make the background pink. The first number, 2, refers to the back¬
ground. The second number, 4, indicates what color the background
will be, and the third number, 6, gives the brilliance or luminance
of the hue. The higher the third number, the greater the luminance.
This number can be any even number from 0 to 14. Some of the
possible color hues and their corresponding numbers are listed in the
table below. See Table 9.3 of the ATARI BASIC Reference Manual
for the complete set of colors available.
Nutnber Color
0 Gray
2 Orange
4 Pink
7 Blue
10 Turquoise
12 Green
The border colors are determined in the same way as the
background colors. To change border colors, use 4 as the first
number in the SETCOLOR statement. The statement SETCOLOR
4,12,6 would give a green border.
Graphics 55
3-4 PRACTICE TEST
1. What figure will the computer draw when you enter the following
direct mode statements?
GRAPHICS 8=COLOR 1
PLOT 160 .. 60 •• DR A WTO 140 .■ 60
DRAWTO 140 .. 1 00 : DRAWT0 1 80 .■ 100
DRAWT0 1 8 0 .. 60 = D R A WTO 160,60
2. What figure will the computer draw when you enter the following
direct mode statements?
GRAPHICS 8 : COLOR 1
PLOT 1 60,80 = DRAWTO 1 40 .■ 1 00
DRAWT 0 1 80 , 1 00 = D R AWTO 160.. 80
PLOT 140,100 •• DRAWTO 140,140
D R A W T 0 18 0 , 140 = 0R ft U| J n 18 0 , 1 0 0
L
3.
Write direct mode statements that will instruct the computer to draw
the following diagram, with the point (160,80) as indicated.
< 1 6@80 >
4. Write direct mode statements that will instruct the computer to plot
the following points in high resolution graphics.
a. The center of the screen.
56 Hands-on BASIC
b. The upper left-hand corner.
L
c. The top center point.
d. The point (240,150).
5. a. How do you get into high resolution graphics mode?
L
b. What color statement should you use if you want to draw an
orange line in low resolution graphics?
6. What does the following program do?
100 GRAPHICS 8
110 LET h=0
120 COLOR 1
130 PLOT 140,A :
140 COLOR 0
150 PLOT 148,A:
168 LET A=R+5
170 GOTO 128
180 END
DRAWTO 288,A
DRAWTO 280,A
CHAPTER 4
COMPUTER ARITHMETIC
AND
PROGRAM MANAGEMENT
4—1 OBJECTIVES
Now that you have learned how to turn on your ATARI computer,
how to bring up ATARI BASIC, and how to communicate with the
computer, you are ready to go on to more interesting tasks. You will
need an ATARI disk drive and a blank diskette for some of these
activities.
Doing Arithmetic on the Computer
Mathematics on the computer calls for only the simplest arithmetic
operations. You will gain a clear understanding of how these arith¬
metic operations are done.
Using farentheses in Computations
You must type all mathematical expressions on a single line to enter
them into the computer. Some expressions can be handled this way
only by organizing parts of the expressions in parentheses. You will
learn to use parentheses effectively.
Using E Notation for Numbers
The computer must deal with both very large and very small num¬
bers. E notation is used by the computer to describe such numbers.
You will learn to recognize and interpret E notation.
58 Hands-on BASIC
Formatting a Diskette
You must prepare or “format" new or blank diskettes for use on your
ATARI computer. You will learn how to format diskettes correctly
in order to store programs.
Storing and Retrieving Programs
You have already seen some commands. You will learn additional
commands that will permit you to store programs on and retrieve
them from a diskette.
4-2 DISCOVERY EXERCISES
1. Turn on your computer and bring up ATARI BASIC. Recall from
Chapter 1 the following symbols for arithmetic operations:
+ Addition
—Subtraction
* Multiplication
/ Division
To review the arithmetic operations, type in the following program:
1 0 0
INPUT ft
110
INPUT B
120
LET C=A
130
PRINT C
140
END
Display the program and study it briefly. If we run the program
now and enter 2 for A and 3 for B, what do you think will be typed
out?
L
Run the program and write down what happened.
Computer Arithmetic and Program Management 59
2. Clear the program in memory. Note that the sy mbol
same key with the * and requires you to use the
type
SHIFT
v is on the
key. Now
100 LET A=3*3
110 LET B=3 A 2
120 PRINT A
130 PRINT B
140 END
Display the program and make sure it is correct. Now run the
program and record what was typed out.
Compare the numbers printed out to the expressions in the lines
where they were computed. Notice that they are essentially the same.
See if you can figure out what is taking place.
3. Type
100 LET £=3*3*3
110 LET B = 3•*'*■ 3
Run the program. What was typed out?
L
4. Type
100 LET R=2*2*2*2
110 LET B=2 A 4
Run the program. What was typed out?
What is the ^ symbol used for?
60 Hands-on BASIC
5. Remember from your introductory algebra course (if you haven't
had algebra, don't panic!) that when you want to multiply 2x2x2
for example, you can indicate this with an exponent. You would
write the expression as
2 3
How would this expression be written in BASIC using the ^ symbol?
(Hint: See steps 2, 3, and 4.)
6. Fill in the operators (symbols) that call for the following arithmetic
operations:
Division
Exponentiation
Multiplication
i_
7. Clear out the program in memory. Type
100 LET A=4+2 £ 6- 3
110 LET B=< 4 + 2 > ♦ 6-*’3
120 LET C = 4 + < 2t€ >-^3
130 LET D=4+2#< 6-*‘3 >
140 PRINT A
150 PRINT B
160 PRINT C
170 PRINT D
130 END
The two points of this program are (1) the order in which the
arithmetic is done, and (2) the effect of the parentheses. If you
look closely, you will see that the same numbers and operations are
involved in each of the calculations in lines 100, 110, 120, and 130.
Computer Arithmetic and Program Management 61
The only difference is the groupings within parentheses. Run the
program and record what was typed out.
Study the program and the numbers the computer typed out until
you see what is taking place in the program. The computer has
established rules for such situations. We will go over these rules
later in the chapter.
8. Clear out the program in memory. Now enter the following pro¬
gram:
100 LET ft = 3*100*100*100
110 LET B=3*100*100*100*100
120 LET C=3*100*100*100*100*100
130 PRINT h
140 PRINT B
150 PRINT C
160 END
Execute the program and record the output.
L
Can you explain the different form in which the numbers were typed
out? (Hint: Count the number of zeros in the multipliers in lines 100,
110, and 120.)
9. Type
100 LET h = 4/10
110 LET B=4-*< 10*10 >
120 LET C=4.--< 10*10*10)
Execute the program and record the output.
Can you understand what is happening in the output? Count the
zeros in the denominators in lines 100, 110, and 120.
62 Hands-on BASIC
10. Explain in your own words what it means when an E shows up in a
number typed out by the computer.
If you still do not fully understand the purpose of the E notation,
don't worry. We will return to it later.
11. Before you can proceed with storing and retrieving programs, you
must format a diskette. (If you do not have a disk drive, go to the
discussion.) Turn off your computer and connect the disk drive (see
steps 1-6 in the first few pages of the Owner's Guide that came with
the disk drive). When you are asked to insert a diskette at step 5
in the Owner's Guide, insert the diskette labeled Master Diskette II
that came in the package.
12. Close the disk drive door. If you removed the BASIC cartridge,
replace it and turn on the computer to bring up ATARI BASIC.
Note: Wait until the the busy light goes off before proceeding.
13. Now type
DOS
and in a short time you will see a "menu" on the screen. This menu
gives you several options.
14. You are now ready to format a diskette and place the DOS files
on it. First replace the diskette in the drive with the diskette to be
formatted. This can be either a new diskette or an old one. Warning:
all programs and information on this diskette will be lost when the
diskette is formatted.
15. We note fro m the me nu that I is the letter you need to select. So type
I and press [RETURN! • Type in 1 and Y, respectively, in response to
the next two questions. After about 45 seconds, the diskette will be
formatted, and the display will again show
SELECT ITEM OR RETURN FOR MENU
Computer Arithmetic and Program Management 63
16. The next menu item you want is H. Type in H and press [RETURN] .
Again, type in a 1 and Y in response to the next two questions. The
computer will display
WRITING HEW DOS FILES
17. To see what files are stored on the diskette just formatted, type in
A and press RETUK
!N| twice. You should now see
_
DOS
S Y S 8 3 9
DUP
SYS 042
-
626 FREE
SECTORS
18. We are now ready to store an d retriev e programs. Get back to
ATARI BASIC by typing B and [RETURN] . Then type in the follow¬
ing program:
100 LET h=£
110 LET B=3
120 LET C=A*B
130 PRINT C
140 END
19. Display the program to make sure it is correct. Run the program.
20. Now type
SAUE 11 D : PRODUCT"
This moves the program in memory to diskette under the name
PRODUCT. You may choose any name of eight characters or less
beginning with a letter.
21. You can obtain the director y of files on this diskette by first typing
DOS and pressing [RETURN! . When the busy light on the disk drive
goes off, type in A and press 1 RETURN] twice. You should now see
that the program PRODUCT has been added to the directory. Is it
there?
64 Hands-on BASIC
22. Get back to ATARI BASIC by typing B and
the memory. Is anything there?
23. Type in the following program.
100 LET D = 2 $ 6 -8/4
110 PRINT D
120 END
Run the program. Think of a name for this program other than
PRODUCT. Limit the name to eight or fewer characters The first
character must be a letter, but the others can be digits or letters.
Record the name below.
Move the program in memory to diskette under the name you have
just chosen. (See step 20.) Now display the program in memory. Is
the program you just saved to diskette still in memory?
24, Obtain the directory of programs stored on diskette (See step 21.)
Are the two programs you just entered there?
Now, you should have stored the two programs you just entered.
The name of the first program is PRODUCT; you wrote the name
of the second in step 22, To simplify the discussion, we will refer
to this second program as PROGRAM 22. You, of course, must use
the name you selected for the second program.
25. Get back into ATARI BASIC with the correct menu selection. To
move PRODUCT from disk to memory, type
LOAD "D : PRODUCT"
Display this program and verify that it is the right one. Now move
PROGRAM 22 from disk to memory. Display the program in
memory. Which one is there now?
RETURN] ■ Now display
Computer Arithmetic and Program Management 65
What happened to the program PRODUCT that was in memory
when you moved PROGRAM 22 into memory from diskette?
Now type
RUN "D:PRODUCT"
What number is displayed on the screen?
L
What program is now in memory?
Display the program to see if you were correct.
26. We now have PRODUCT in memory. Remove the program
PRODUCT from diskette by typing DOS. Then select D from the
menu and in response to
DELETE FILE SPEC
type in PRODUCT. Then type in a Y in response to
TYPE "Y" TO DELETE
D1 PRODUCT ?
27. Obtain a directory of the programs stored on diskette. PRODUCT
should not be there, but PROGRAM 22 should be. Inspect the listing
of programs. Is everything the way it should be?
L
28. Get back to ATARI BASIC. Now try to move PRODUCT from disk
to memory. (See step 25.) What happened?
66 Hands-on BASIC
Error 170 means the file is missing. Clear out PROGRAM 22 from
the diskette. (See step 26.) Turn off the computer.
4-3 DISCUSSION
Doing Arithmetic on the Computer
We are concerned with five arithmetic operations. These are ad¬
dition, subtraction, multiplication, division, and exponentiation
( + , —, *, /, ^). The first four are familiar to you. The last
(exponentiation) may be unfamiliar, but is not nearly as complicated
as its name suggests.
The exponentiation operation is represented by the ^ symbol.
Exponentiation merely means "raised to the power.Therefore, 3^4
means "3 raised to the fourth power," or 3x3x3x3, giving 81 as the
result. (The computer actually gives 80.99999834 due to the way it
handles exponentiation.)
You need to understand the order in which the computer
performs arithmetic operations. Consider the following expression:
2 +3^2/5 — 1
If the computer simply performed operations starting at the left as
they occur in the expression, it would add 2 plus 3 (giving 5), raise
5 to the second power, (giving 25), divide by 5 (giving 5), and sub¬
tract 1 producing an answer of 4. However, suppose addition and
subtraction are done first, then exponentiation, then multiplication
and division. This order would give 5 raised to the second power
(25) divided by four, for an answer of 6.25.
Different rules for the order of arithmetic operations could
produce other answers. However, there are well-defined rules in
BASIC for the order and priority of arithmetic operations. They
are:
Operations are performed from left to right, using the follow¬
ing priority rules.
The priority for arithmetic operations is
1. Exponentiation
2. Multiplication and division
3 Addition and subtraction
Now going back to the example:
Computer Arithmetic and Program Management 67
2 + 3^2/5-l
First you scan left to right for exponentiation. Since there is an
exponentiation indicated (3^2), it is done first. Now the expression
is:
2+9/5-1
You scan from left to right for exponentiation again, and finding
none, look for the operations with the next highest priority, multi¬
plication and division. The division is therefore done next, with the
following result:
2 + 1 . 8-1
Since there are no more multiplications or divisions in the expres¬
sion, you scan from left to right for addition and subtraction. The
addition gives
3.8-1
and the final subtraction produces the answer of 2.8.
Review the rules for order and priority of arithmetic opera¬
tions until they become second nature to you.
Using farentheses in Computations
The rules for order and priority are not the whole issue in arithmetic
operations. Consider the following example:
■B -.
r A n
(2*3 +4~2'
*2+5;
*(3~2-4)
The difference between this expression and the ones you have been
studying is that parentheses are used here to group parts of the
expression. We will go through this example in great detail to show
you how the computer attacks the arithmetic.
68 Hands-on BASIC
The computer starts by scanning from left to right and meets
the left parenthesis of B. It then looks inside to see if there are any
more left parentheses and finds the one for A. The next parenthesis
met is a right parenthesis for A. At this point, the computer has
isolated the first group of operations to be done. This is:
2*3 +4^2
and is evaluated using the order and priority rules. The result is 22
(check it). Now the problem has become:
B _
(22*2+5
3^2-4)
On the next scan, the computer isolates the right parenthesis of B,
does the arithmetic inside, and the problem is now
49*(3~2-4)
Since there are only the C parentheses left, the computer does the
arithmetic inside, giving
49*5
which produces the answer of 245.
Thus, if parentheses are nested, the computer works out from
the deepest set, scanning from left to right. When a set of parentheses
is removed, the arithmetic operations inside are done according to
the order and priority rules given in the preceding section. A very
good rule of thumb for the beginner is to use extra parentheses if
there could be any confusion about how the computer will evaluate
an expression. Too many cannot hurt, but too few certainly can.
Using E Notation for Mumbers
BASIC prints numbers in different forms. In particular, BASIC uses
the E notation for very large or very small numbers. Examples of
the E notation are 2.145E + 06 or 6.032E~07.
Computer Arithmetic and Program Management 69
The reason you need this special notation is that the computer
usually prints out only nine digits for a number. A problem arises
if you want to print out a variable whose value is 45612800000,
eleven digits. The computer will print this out as 4.56128E + 10.
The E + 10 means that the decimal point belongs ten places to the
right of its present position. You can express very small numbers in
the same way. A variable whose value is 0.0000000683 would be
printed out as 6.83E —08. The E—08 means that the decimal point
belongs eight places to the left. The table below should help you
understand how to convert from decimal to E notation or from E
notation back to decimal notation.
Decimal Form
E Notation
2630000
2.63E + 06
263000
2.63E + 05
26300
2.63E + 04
2630
2.63E + 03
263
2.63E + 02
26.3
2.63E + 01
2.63
2.63
0.263
2.63E-01
0.0263
2.63E-02
0.00263
2.63E-03
0.000263
2.63E-04
0.0000263
2.63E-05
0.00000263
2.63E-06
To change from E notation to decimal notation, look at the
sign following the E. If the number is + , move the decimal point to
the right as many places as the number. If the sign after the E is
move the decimal point to the left. To convert from decimal to E
notation, just write E + or — however many places the decimal has
moved left or right, respectively.
Actually, you shouldn't get very tense about the E notation,
since you will rarely use it. The main reason for bringing it up
is that the computer may print out numbers in the E notation.
Consequently, you should be able to recognize what is happening.
Formatting a Diskette
As you saw in the discovery exercises, formatting a diskette (new or
old) is a straightforward task. With the computer turned off, you
turn on the disk drive. When the busy light goes off, you place the
70 Hands-on BASIC
Master Diskette II into the drive and close the door. (Note: Make a
copy of this diskette so that you can use the copy and preserve the
original. See An Introduction to the Disk Operating System , page
12). Then you turn on the computer. DOS will be loaded. If the
BASIC cartridge is not in place, the menu of disk drive operations
will appear on the screen. If the BASIC cartridge is in place you
can display the menu of disk drive operations by typing in DOS.
At this point, you replace the diskette in the disk drive with the
one to be formatted. To accomplish this, select I from the menu,
1 for the disk drive request, and Y to complete the process. This
clears all programs and information from the diskette. Copying the
DOS files to a formatted diskette will allow you to get back and
forth between disk operations and BASIC. To copy the DOS files
right after formatting the diskette, select H from the menu and again
respond with 1 to the disk drive request, then with Y to complete
the process.
Storing and Retrieving Programs
When you turn off the computer, you lose the program in memory.
If every time you turned on the computer, you had to type in pro¬
grams you wanted to use, you would get very little work done.
Fortunately, with the ATARI computer you can type in long or com¬
plicated programs, troubleshoot them, and then store the programs
on a formatted diskette for future use. To retrieve a stored program
you need only turn on the disk drive, place the disk you need into
the drive, turn on the computer, and bring up ATARI BASIC.
When you wish to save a program on diskette, you need to
give it a name. You can use any name provided it starts with a letter
and is eight characters or less. From the second character on, any
letter or digit may be used in the name. For instance, you could
use PRODUCT or TEST1. You should choose meaningful names to
help you remember what each particular program does.
■ To move a program from memory to diskette, type
SAVE "D: (name of program/'
To move a program from diskette storage to memory, type
LOAD "D: (name of program/'
Computer Arithmetic and Program Management 71
■ To move a program from diskette storage to memory and
execute it, type RUN "D: (name of program/'
You might not want to keep a specific program on a diskette
forever. The disk drive operations menu provides a way to clear pro¬
grams from diskette storage. To clear out a program on a diskette,
select the appropriate letter in the menu of the disk drive operations
menu . As you have seen you can obtain this menu by typing DOS
and RETURN . You can get back to ATARI BASIC by selecting B
from the menu.
You must be very careful when using the SAVE command.
For instance, suppose you wish to move a program from memory to
diskette and inadvertently type
SAME 11 D : PRODUCT 11
If PRODUCT is the name of another program saved on the diskette
in the disk drive, then the program on diskette will be replaced by
the program in memory. This is fine if the program in memory is
an update of the program on diskette. If not, however, you have
destroyed a program you wanted to keep. You can avoid this kind
of problem by making back-up or spare copies of diskettes. Keeping
a record of all the files you save on a diskette can also help you avoid
this situation.
4-4 PRACTICE TEST
1. Write down the symbols used to signify the following arithmetic
operations in BASIC expressions:
a. Multiplication
i_
b. Exponentiation
c. Division
72 Hands-on BASIC
2. When evaluating arithmetic expressions, what is the computer's
priority of operations?
a. First
b. Second
c. Third
3. When the computer scans arithmetic expressions, in what direction
does it search?
i_
4. Write a BASIC statement equivalent to the following expression.
Number the line 100.
A = (4 + 3 B/Df
L
5. If the computer runs the following program, what will it type out?
100 LET A = 2
110 LET B=3
120 LET C=< A*B+2V2
130 PRINT C
140 END
L
6. Convert the following numbers to E notation:
a. 5160000
Computer Arithmetic and Program Management 73
b. 0.0000314
I _
7. Convert the following numbers to decimal notation.
a. 7.258E + 06
i_
b. 1.437E-03
I_
8. In the expression below, give the order in which the computer will
perform the operations,
100 LET A = < 6 / 3+4 } 2
i_
9. What commands does the computer need to carry out the following
operations?
a. Moving a program from diskette storage to memory
i_
b. Moving a program from memory to diskette storage
i_
c. Clearing out a program in diskette storage
i_
d. Clearing out a program in memory
i_
e. Displaying the program in memory
74 Hands-on BASIC
f. Executing the program in memory
g. Displaying the names of all the files saved on diskette
L
10. Suppose you are typing a line into the computer and have not yet
pressed RETURN. How do you correct a single character?
CHAPTER 5
INPUT AND OUTPUT
5-1 OBJECTIVES
In this chapter you will get down to the business of writing programs.
You will also increase your knowledge of BASIC by looking at some
details about input and output.
Getting Numbers into a BASIC program
There are only three ways to enter numbers into the computer for
a BASIC program. Since the computer is concerned mainly with
numbers, you need to understand how to input these numbers.
Printing out Variables and Strings
After information is computed, it must be printed out. There are
different kinds of output, but usually you will want to output strings
of characters as well as numbers. This string output is handled
essentially the same as numbers, but needs special attention.
Spacing the Printout
The computer has a built-in spacing mechanisms, but you can use
punctuation to signal the computer to space output as you desire,
for legibility and sense.
Using the REM Statement
The wise programmer includes comments in programs to help ex¬
plain or interpret what is being done. The REM statement in BASIC
lets you do this.
76 Hands-on BASIC
Working with Program Examples
Your ultimate goal is to learn how to write and troubleshoot pro¬
grams. In this chapter you will begin with some simple program
assignments.
5 — 2 DISCOVERY EXERCISES
1. Turn on the computer and bring up ATARI BASIC. Enter the fol¬
lowing program:
108 INPUT A
110 INPUT B
128 INPUT C
130 LET B=A+B+C
140 PRINT D
150 END
What do you think will happen if you run this program?
L
Run the program. When the first question mark appears, (the INPUT
prompt for A), type in 2. Likewise, when the second question mark
appears, type in 3, and finally, at the last question mark, type in 5.
Record the output.
2. Note that in the program in step 1 we have three INPUT statements
(lines 100, 110, and 120). Type
1 0 0
110
What does this do to the program?
Input and Output 77
Display the program in memory and see if you are right. Then type
120 INPUT A,B,C
Display the program. What happened?
L
3. Run the program and when the INPUT prompt (?) appears, type in
What happened?
Can you input more than one variable at a time in a BASIC program?
L
4. Run the program, and when the INPUT prompt appears type
What happened?
L
What is the computer waiting for?
Type
What happened?
78 Hands-on BASIC
5. Run the program and when the INPUT prompt appears, type
2,3,5 , 1
What happened?
I_
6. Can you type in more numbers than are called for at an INPUT
statement?
i_
What will happen if you do?
i_
7. Can you type in fewer numbers than are called for at an INPUT
statement?
i_
What will happen if you do?
i___
8. Type
120 READ A.B,C
Display the program. What happened?
i___
Run the program and record the output.
Error 6 means the computer is out of data.
Input and Output 79
9. Now type
125 DATA 2,3,5
and display the program. What happened?
i_
10. Run the program and record the output.
Based on what you have just seen, when a BASIC program contains
a READ statement, there must be another type of statement in the
program. What is that statement?
11. Name two different methods (other than using a LET statement) for
getting numbers into a program. (Hint: See steps 1 and 8.)
i_
12. Display the program in memory. Delete the DATA statement (line
125). Type
145 DATA 2,3,5
and display the program again. What happened?
i___
13. Run the program and record the output.
Does it make any difference where the DATA statement is in the
program?
80 Hands-on BASIC
14. Clear the program in memory. Enter the program below
100 READ A,B
110 LET C = R.‘*'B
120 PRINT C
13 0 G 0 T 0 1 0 0
1 40 DATA 2, 1,6, 2 , 90 , 9,35,7
150 END
What do you think will happen if you run the program?
Try it and see if you were correct. Record the output.
i_
Is the Error 6 (out of data) message associated with the READ
statement or the DATA statement?
15. Delete the DATA statement in line 140 from the program, and enter
the following statements:
105 DATA 10,2
115 DATA 100,50
125 DATA 50,5
Display the program in memory. What happened?
16. If you run the program, what do you think will be displayed?
i_
Run the program to see if you were correct. Record the output.
Input and Output 81
17. Can you have more than one DATA statement in a BASIC program?
Does it make any difference where the DATA statements are in the
program?
18. Clear out the program in memory. Enter the following program:
100 LET H=10
110 PRINT A
120 END
What will happen if you run this program?
Run the program and record the output.
19. Now type
110 PRINT "A"
and display the program in memory. What happened?
What will happen if you run the program?
Run the program and record the output.
82 Hands-on BASIC
20. Type
lie PRINT "HOUND DOG = ";A
and display the program in memory. What do you think will happen
if you run this program?
Run the program and record the output.
21. Type
110 PRINT "B = ";A
Display the program and study it carefully. What do you think will
happen if you run the program?
Try it and see if you were right. Record the output.
22. Type
95 REM DEMO PROGRAM
Display the program. What happened?
Run the program, and record the output.
Does the REM statement in line 95 have any effect on the program?
Input and Output 83
23. Clear out the program in memory. Enter the following program:
100 REM METRIC CQNUERSIOH PROGRAM
110 REM CONVERT LBS. TO GRAMS
120 PRINT "INPUT NO. OF LBS. ";
130 INPUT P
140 LET G=454*P
150 PRINT P; n POUNDS IS ";G;" GRAMS"
160 GOTO 120
170 END
Display the program to see if it is correct. Note the semicolons.
Study the program carefully and try to guess what will happen if
you run it. Run the program. When the INPUT prompt is typed out,
enter any number you desire. Note what is typed out. Repeat this
process several times, then jump the computer out of the INPUT
loop. If you have forgotten how, see Chapter 2, step 21 of the
discovery exercises. What is the purpose of the REM statement?
24. Type
115 INPUT P
130
160 G 0TO 115
and then display the program in memory. What happened?
Will the program work in this form?
Run the program and at the INPUT prompt, type 1. What hap¬
pened?
Jump the program out of the INPUT loop.
84 Hands-on BASIC
25. Clear the program in memory and enter it again, modified as follows:
1 00
REM METRIC COHUER
SION PROGRAM
110
REM CONVERT LBS.
TO GRAMS
120
PRINT "INPUT NO.
OF LBS . "
130
INPUT P
140
PRINT P; "POUNDS I
S "jG;"GRAMS
150
LET G=454*P
160
GOTO 120
170
END
Can you run the program in this form?
Run the program and at the INPUT prompt, type 2. What hap¬
pened?
What is wrong. Remember that if a variable is not defined in your
program, your computer will define it as 0.
Jump the program out of the INPUT loop.
26. Clear out the program in memory. Enter the following program:
100 READ A
110 PRINT A
120 GOTO 100
130 DAT A 10,12,8, 3 ,73,60,82
140 END
Run the program and record the output.
Input and Output 85
27. Type
110 PRINT A,
Note that all you have done is to insert a comma after the A in line
110. Execute the program and record the output.
28. Replace the comma after A with a semicolon by typing
110 PRINT Ai
Run the program and record the output.
29. If a variable in a PRINT statement is not followed by any punctua¬
tion marks, what happens after the number is printed out? (Hint:
See step 26.)
Suppose the variable is followed by a comma?
What happens if the variable is followed by a semicolon?
i_
30. This concludes the computer work for now. Turn off the computer.
5-3 DISCUSSION
In this chapter you have begun to get away from the mere mechanics
of controlling the computer and to concentrate more on writing
and troubleshooting programs. This skill doesn't come naturally to
most people, and consequently we will give the topic a great deal of
attention, both now and in later chapters.
86 Hands-on BASIC
Getting Numbers into a BASIC Program
In Chapter 1 you learned that one way to get numbers into a program
is to assign values to a variable in the program itself. For example,
100 LET
introduces the value 6 into a program and stores the number under
the variable name A. This method has limitations, but there are two
other ways to get numbers into a BASIC program: INPUT statements
and READ and DATA statements. Let's look first at the INPUT
statement and how it is used.
When the computer runs a line such as
260 INPUT G
it will type out a question mark as a prompt that input is expected
from the terminal, then it will stop and wait for you to type in the
number. In the case above, the number typed in will be known as
G.
An INPUT statement may call for more than one variable. For
example,
420 INPUT h,B,C,D
In this case the computer uses the same INPUT prompt (?) but
now you must type in four numbers separated by commas. If you
enter fewer than four and press the RETURN key, the computer will
type another question mark and wait for the remaining numbers to
be input. If you enter more than four numbers, the program will
continue running using only the first four numbers you typed in.
The last method of providing numerical input is to use the
READ and DATA statements. The computer handles the statement
100 READ h,B,C,D
the same way it handles an INPUT statement with two exceptions.
First, the computer does not stop, and second it reads the numbers
called for from DATA statements in the program.
Consider the following program:
1 0 0 READ A.. B « C .■ D
110 LET E=A+B+C+D
Input and Output 87
120 PRINT E
130 DATA 25,3,17,12
140 END
The program reads the four numbers from the DATA statement and
prints out the sum of the numbers. It makes no difference where
the DATA statement is in the program. There can be more than one
DATA statement, and they need not be grouped at the same place in
the program. Because numbers are called for by READ statements,
they are taken in order from the DATA statements, beginning with
the lowest-numbered statement. If you need more numbers than are
available in DATA statements, the computer will type
ERROR - 6 AT LINE <line #>
and then halt. Recall that many of the error messages are sum¬
marized on the inside of the cover.
You will become familiar with the advantages and disad¬
vantages of each of these methods as you spend more time writing
programs.
■ You can put numbers into a BASIC program with:
(1) LET statements; (2) READ and DATA statements; and
(3) INPUT statements.
Printing out Variables and Strings
Output from the computer is quite simple. The computer can print
out either the numerical value of a variable or a string of characters.
To illustrate, suppose we have a variable named X and the number
2 is stored in that location. The program
1 0 0
LET X
110
PRINT
120
PRINT
130
END
shows the difference between string and variable output. Line 110
prints out the character X, because X is enclosed in quotation marks.
Line 120 prints 2, because that is the number stored in location X.
88 Hands-on BASIC
The rule is clear. Any set of characters contained within
quotation marks is called a string. The computer prints out strings
exactly as they are listed; it does not attempt to analyze or detect
what is in the string. The computer prints out the numerical value
of any variable that is not in quotes.
It is possible to do computations with a PRINT statement.
Thus
100 PRINT A+B+CjD
will cause the computer to print out the sum of the numbers stored
in A, B, and C and the number stored in D. Of course, the variables
A, B, C, and D would have to be defined or the computer will assign
zeros for their values.
Spacing the Printout
BASIC has a built-in standard spacing mechanism that prints four
numbers equally spaced on one line. Where possible, this standard
spacing is used by the computer when quantities in a PRINT state¬
ment are separated by commas. The comma signals the computer
to move to the next print position on the line. If the computer is
already at the last position on a line and encounters a comma in a
PRINT statement, it does a carriage return and prints the number
on the first position on the next line. Thus
100 PRINT h,B,C,D,E
would cause the numerical values of A, B, C and D to be printed
equally spaced across a line in the four standard positions. The
numerical value of E would be printed on the next line and indented
two spaces. If four or more numbers are to be printed and if one of
the numbers has more than eight digits, then the number of columns
will be reduced to three.
■ Commas in PRINT statements produce 4 columns per line.
Another type of spacing is produced by the semicolon between
variables. For example, in the statement
100 PRINT h;E;C
Input and Output 89
the numbers will be printed close together and space needs to be
provided. However, such spacing is relatively easy to do. For
example, the direct mode statement
PRINT ft} 11 H ;B
will produce a single space between the two numbers
The semicolon can also be used in an INPUT statement to
cause the program to stop and place the input prompt at the end of
the statement. For example, when the statement
130 PRINT "WHAT IS THE PRICE? ";
is executed, the input prompt will be placed at the end of the question
and await your input.
You can add vertical spacing to output by using an empty
PRINT statment as follows:
100 PRINT
The computer looks for the quantity to be printed and finds none.
It then looks for punctuation and, finding none, orders a carriage
return and moves the cursor down one line. You can add as many
empty lines to the printout as you wish by using empty PRINT
statements.
Using the REM Statement
The REM (“remark”) statement is different from the statements you
have seen previously. As soon as the computer encounters the
characters REM following the line number, it ignores the balance
of the statement and goes on to the next line. The REM statement
simply provides information to help the programmer or someone
reading the program to follow what is happeneing in the program.
The wise programmer will use REM statements liberally.
Below we present the same program with and without REM
statements. You can decide which program is easier to follow.
With REM statements:
100 REM COMPUTE AVERAGE OF FOUR NUMBERS
110 REM INPUT THE FOUR NUMBERS
120 INPUT A,B,C,D
90 Hands-on BASIC
130 REM COMPUTE THE AVERAGE
148 LET X = < A + B+C+D >-"4
150 REM PRINT OUT THE AUERAGE
160 PRINT X
170 END
Without REM statements:
100 INPUT A,B,C,D
110 LET X = < A + B + C + D >-*‘4
120 PRINT X
130 END
■ You can describe what is happening in a program
with a REM statement.
5 — 4 PROGRAM EXAMPLES
Study each of the following examples until you are certain you
understand all the details. You might want to enter the programs
into the computer and run them to verify that they work as intended.
Example 1 - Unit Prices
Your problem is to write a program to compute unit prices of su¬
permarket items. If you let T stand for the total price, N for the
number of units, and U for the unit price, you can compute the unit
price with the following relationship:
U = T/N
For example, if a case of twelve large cans of fruit juice costs $6.96,
the unit cost per can would be:
U = 6.96/12 = $0.58
You want the program to produce the following output:
WHAT IS THE TOTAL PRICE? (You enter value of T)
NUMBER OF UNITS? (You enter value of N)
UN IT PRICE I S (Computer types out value of U)
Break the example apart to see how the program is related to
what you want to see in the output.
Input and Output 91
WHAT IS THE TOTAL PRICE? (entry of T)
100 200
NUMBER OF UNITS? (entry of N)
300 400
500: Compute unit price.
UNIT PRICE IS (output of U)
600 700
You will write each line of the program so that the numbers
below each statement will be the line numbers in the program. In
line 100 you will use the PRINT command to tell the computer to
type out the message indicated.
108 PRINT "WHAT IS THE TOTAL PRICE? n
Note the semicolon outside the closing quotation marks. The reason
for this is that you do not want a carriage return; you want the
printed line to hold there for the INPUT prompt on line 200:
200 INPUT T
Use a PRINT statement to get the computer to print out the message
in line 300.
300 PRINT "NUMBER OF UNITS? ";
Handle the input for the total number of items the same as the total
price.
400 INPUT N
Next you compute the unit price in line 500.
500 LET U=T "N
Use a PRINT statement to handle the next line, a message followed
by the unit price.
600 PRINT "UNIT PRICE IS ";U
92 Hands-on BASIC
Finally, add an END statement.
700 END
Now put the whole program together.
100 PRINT "NHAT IS THE TOTAL PRICE? " ;
200 INPUT T
309 PRINT "NUMBER OF UNITS? ";
400 INPUT N
500 LET U=T/N
600 PRINT "UNIT PRICE IS "jU
700 END
Study the program to make sure you see the purpose of each
line as related to the original statement of the problem.
Example 2 - Converting Temperature
The relationship between temperature measured in degrees Fahren¬
heit and in degrees Celsius is
C = (5/9)(F - 32)
where C stands for degrees Celsius and F stands for degrees
Fahrenheit. If, for example, F is 212, then C is
C = (5/9)(212 - 32) = 100
As in the first example, you will write the program after
deciding how you want the output to appear. Suppose you want
to see the following:
INPUT NO. OF DECREES F
? (You enter value of F)
(Value of F) DEGREES F IS (answer) DEGREES C
Split the output up into parts that will be generated by the lines in
the program.
Input and Output 93
INPUT NO. OF DEGREES F
100
200: Entry of F
300: Compute C
(Output of F) DEGREES F IS (Output of C) DEGREES C
400
The corresponding program is
100 PRINT 11 INPUT NO. OF DEGREES F"
208 INPUT F
300 LET C = < 59 >$(. F-32 >
400 PRINT Fi" DEGREES F IS ” ;C;" DEGREES C"
500 END
This program is a bit different from the first example. In
line 100 there is no puncuation following the string. Thus the
INPUT prompt generated by line 200 will be printed out on the
line following the initial string. The PRINT statement in line 400
prints out (1) the value of F, (2) a string, (3) the value of C, and (4)
a second string. The semicolons in line 400 are used to put space
between the variables and strings in the PRINT statements.
Example 3 - Sum and Product of Numbers
Suppose you want to compute the sum and product of two numbers,
when the program is run, you want to see:
INPUT A? (You enter value of A)
INPUT B? (You enter value of B)
SUM OF A AND B IS (Computer prints out sum)
PRODUCT OF A AND B IS (Computer prints out product)
(Blank lines are inserted by the computer.)
INPUT A? (You enter a second value of A)
(etc.)
Since you studied the first two examples in great detail, you
can proceed more rapidly with this problem. The first line of the
output can be handled by the following statements:
100 PRINT "INPUT A
110 INPUT A
1! .
94 Hands-on BASIC
Note that the message printed out in line 100 is window
dressing for the program and has nothing to do with the actual
calculations. The input instruction that is important to the computer
is in line 110. However, such messages are important to you because
they tell you what to do. You can generate the second line of desired
output in the same manner.
120 PRINT 11 INPUT B
130 INPUT B
Use the following lines to generate the sum and product of the two
numbers.
140 PRINT "SUM OF A AND B IS
150 PRINT "PRODUCT OF h AND B IS "A*B
The spacing between the output of the original set of numbers and
the output obtained when the program loops back, as well as the
looping instructions, can be obtained with three statements.
160 PRINT
170 PRINT
180 GOTO 100
Of course, the final line should be the END statement.
190 END
The whole program is:
1 00
PRINT
"INPUT h
H .
110
INPUT
A
120
PRINT
"INPUT B
il .
130
INPUT
E:
140
PRINT
"SUM OF h
h AND
150
PRINT
"PRODUCT
OF A
160
PRINT
170
PRINT
180
GOTO
100
190
END
A*B
You could also compute the sum and product of the two
numbers using LET statements as in the following version.
Input and Output 95
100
PRINT
"INPUT A
li .
110
INPUT
R
120
PRINT
"INPUT B
il .
130
INPUT
E:
140
LET S
= R + B
150
PRINT
"SUM OF f
1 RND
160
LET P
=A*B
170
PRINT
"PRODUCT
OF A
180
PRINT
190
PRINT
2 0 0
6 0 T U
1 0 0
210
END
Both forms of this program will keep looping back until you
jump the the program out of the INPUT loop.
5-5 PROBLEMS
1. Write a program that will read the four numbers 10, 9, 1, and 2
from a DATA statement, putting the numbers in A, B, C, and D,
respectively. Add the first two numbers putting the sum in S. Then
compute the product of the last two numbers, putting the result in
P. Print out the value of S and P on the same line.
2. Write a three line program that will call for the input of four numbers
and then print back the numbers in reverse order. For example, if
you type in 5, 2, 11, 12, the computer should type back 12, 11, 2,
5. The program must work for any set of four numbers that you
decide to type in. Use only three lines in your program.
3. Write a program to read variables A, B, C, and D from numbers
of your choice in a DATA statement and print out the numbers
vertically.
4. What will be output if you run the following program?
100 READ >i,Y,Z
110 DATA 2,5,3
120 LET T=K*Y+Z
130 LET S=Y A 2
140 PRINT T,S
150 END
96 Hands-on BASIC
5. What is wrong with this program?
100 LET A=2
110 READ E:
120 LET A=A+C/B
130 DATA 3
140 PRINT A
150 END
6. Explain in your own words what the following program does.
100 INPUT A,B
110 LET S=A+B
120 LET T=A-B
130 LET U=A*B
140 PRINT S,T,iJ
150 END
7. One of the ratios used to judge the health of a business is the acid-test
ratio. The acid-test ratio is the sum of cash, marketable securities,
and receivables, divided by current liabilities. Write a program that
requests input of the necessary quantities and computes and outputs
the acid-test ratio.
8. Write a program to count and print out by fives beginning with 0.
The first few numbers will be 0, 5, 10, 15, and so on. Interrupt the
program manually when 40 or 50 numbers have been printed out.
9. The intended output of the program below is 1, 3, 5, 7, 9, and so
forth. The program below has an error. What is wrong?
100 LET A=1
110 PRINT h.;" " ;
120 LET A = A + 2
1 3 0 G 0 T 0 10 0
140 END
10. If an object is dropped near the surface of the earth, the distance it
will fall in a given time can be determined by
S = 16T~2
Input and Output 97
where S is the distance fallen (in feet) and T is the time of fall (in
seconds). Write a program that, when executed, will produce the
following output:
TIME OF FALL (SEC) ? (You enter T)
OBJECT FALLS (Computer types out S) FEET
11. The volume of a box can be computed as
V = LWH
where L, W, and H are the length, width, and height. If these are all
measured in centimeters, for example, the volume will be in cubic
centimeters. You want a program that will produce the following
output:
LENGTH < CM > ? (You enter L)
M ID T H < C M > ? (You enter W)
HEIGHT < CM > ? (You enter H)
UOLUME IS (Computer types out V) CUBIC CM
The program below is incorrect and will not produce the output you
want. What is wrong?
1 0 0
PRINT
"LENGTH
< CM >
" L
110
PRINT
"WIDTH <
CM) "
M
120
PRINT
"HEIGHT
<: cm >
" H
130
INPUT
L, U, H
140
LET U =
Ltm-H
150
PRINT
"UOLUME
I s "
160
PRINT
H
170
PRINT
"CUBIC C
M"
180
END
12. In the program below, the INPUT statement calls for two numbers,
A and B. Supply the missing statements so that when A and B are
printed out, the values have been interchanged.
180 INPUT A,B
110
120
130
98 Hands-on BASIC
148 PRINT R,B
150 END
13. Suppose the odometer on your car reads Ri miles when the gas tank
is full. You drive until the odometer reading is R 2 at which point G
gallons of gasoline are required to fill the tank. The miles per gallon
you get on the trip is
M = (R 2 -Ri)/G
Write a program to figure out the mileage for the following data:
Rx R 2 G
21423 21493 5
05270 05504 13
65214 65559 11.5
14. There is an old tale of a wise man who invented the game of chess
and as a reward asked to receive 1 grain of wheat on the first square
of the chess board, 2 grains on the second, 4 grains on the third, 8 on
the fourth, and so on. Write a program to print out the number of the
square and the number of grains on that square. The program should
involve a loop using a GOTO statement and should be interrupted
at the keyboard when you have seen enough. How many grains of
wheat will be on the 64th square? Run the program and find out.
15. It is known that a DATA statement contains examination grades
for a class of ten students. Write a program of no more than four
statements (counting the DATA and END statements) to compute
and print out the class average. Try out the program on sample
data of your choice.
16. Simple interest on an investment is computed according to the fol¬
lowing rule:
I = (P)(R/100)(T/365)
where P is the principal invested at an annual interest rate R
(expressed in percent) for a time T (expressed in days). Write a
program that will generate the display shown below:
Input and Output 99
WHhT IS THE PRINCIPAL
? (You type in the principal)
WHAT IS THE ANNUAL INTEREST RATE < >
? (You type in the interest rate)
WHAT IS THE TERM IN DAYS
? (You type in the term)
FOR AN INVESTMENT OF
(Computer types out the principal)
AT AN ANNUAL INTEREST RATE OF
(Computer types out the rate)
PERCENT INVESTED FOR
(Computer types out the term)
DAYS, THE INTEREST IS
(Computer types out the interest)
17. If compound interest is paid, the true annual interest rate is higher
than the nominal rate which is quoted for the investment. The
following BASIC formula computes this true annual interest rate:
T = ((l+R/(100*M)rM-l)*100
In this expression, T is the true annual interest rate in percent, R is
the nominal interest rate in percent, and M is the number of times the
interest is compounded per year. Write a program that will produce
the following output:
QUOTED INTEREST RATE CPERCENT)
? (You type in the interest rate)
NUMBER OF TIMES COMPOUNDED PER YEAR
? (You type in times computed)
TRUE ANNUAL INTEREST RATE IS
(Computer types out answer)
18. If an amount of money P is left to accumulate interest at I percent
compounded J times per year for N years, the value of the investment
will be
T = P*(l+I/(100*Jr(J*N)
100 Hands-on BASIC
Write a program that will call for the input of P, I, J and N. Run the
program as needed to get the value of $1000 invested at 8 percent
for 2 years compounded
a. Annually (J = 1)
b. Semiannually (J = 2)
c. Monthly (J = 12)
d. Weekly (J = 52)
e. Daily (J — 365)
If a savings and loan company conducts a big advertising campaign
about computing interest every day instead of each week, should
you get excited?
19. If an amount of money P is left to accumulate interest at a rate of I
percent per year for N years, the money will grow to a total amount
T given by
T = P*(l+I/100rN
As an example, if P — $1000, 1 — 6 percent, and N = 5 years,
T = 1000*(1 + 6/100)^5 = 1338.23
Write a program that when executed will produce the following
output:
INITIAL INVESTMENT ? (You enter P)
ANNUAL INTEREST RATE < * > ? (You enter I)
YEARS LEFT TO ACCRUE INTEREST ? (You enter N)
TOTAL VALUE IS (Computer types out T)
5-6 PRACTICE TEST
1. What will be the output if you run the following program?
100 LET X =1
110 PRINT X,
120 LET X=X +1
130 GOTO 110
140 END
Input and Output 101
2. Describe three ways you can put numbers into a BASIC program.
L
3. In a PRINT statement, what is a collection of characters between
quotation marks called?
4. What is the purpose of the REM statement?
L
5. If there is a READ statement in a BASIC program, what other type
of statement must also be present in the program?
L
6. What will happen if you run the following program?
1 0 0
LET X=
~2
110
LET Y=
4
120
PRINT
" Y
_ ii
130
END
7. How many standard print columns per line are provided for in
BASIC when the print quantities are separated by commas?
8. How many DATA statements can you put in a program?
102
Hands-on BASIC
9. What will the output look like if you run the following program?
1 00
LET A =
1
110
LET B =
“7
120
PRINT
A
130
PRINT
A
140
END
10. Suppose you're running the program:
100 INPUT h,B
110 LET C=h+B
120 PRINT C
130 END
In response to the INPUT prompt you type the numbers 10, 12, and
13 on the same line. What will be printed out?
11. You can convert miles to kilometers by multiplying by 1.609. Thus,
10 miles equals 16.09 kilometers, and so on. Write a program that
will produce the following printout.
INPUT NO OF MILES? (You type in a number)
(Computer types your number) MILES EQUAL
(Computer types answer) KIL0METE RS
CHAPTER 6
DECISIONS AND
BRANCHING
6—1 OBJECTIVES
The power of the computer rests in large part on its ability to
make decisions about quantities in programs. In this chapter we
will explore this cabability and will continue the task of learning to
program in BASIC.
Making Transfer Decisions in Programs
Decisions made in programs can cause the computer to jump to line
numbers out of numerical order. Such a transfer to a program line
may be unconditional or may depend on values of variables in the
program. You will learn to use these conditional and unconditional
transfer statements to make simple programs produce powerful and
useful results.
Working with Program Examples
As in the previous chapter, you will continue to learn how to apply
the techniques you study to BASIC programs.
Finding Errors in Programs
When first written, almost all programs have errors. You will learn
the vital skill of troubleshooting programs.
104 Hands-on BASIC
6-2 DISCOVERY EXERCISES
1. Turn on the computer, bring up ATARI BASIC and enter the fol¬
lowing program:
100 LET X=1
110 PRINT X
120 LET K=K +1
130 IF X<5 THEN 110
140 END
The < symbol in line 130 means “less than"; thus, the statement
means as “If X is less than 5 then print X." Study the program
carefully. What do you think will be printed out if you run the
program?
i_
|
Run the program and record the output.
L
2. Now type
100 LET X=2
Display the program in memory. What will the output be now?
L
Run the program and write down what the computer printed out.
3. Now make another change in the program to see if you understand
what is happening. Type
120 LET H=X+2
Display the program and study it carefully. What do you think the
program will do now?
Decisions and Branching 105
Run the program and see if you were right. Record the output.
4. To explore a new idea, you need to make some changes in the
program now in memory. Modify the program to make it agree
with the one below or clear the program in memory and enter the
one below.
1 0 0
LET X=
1
1 10
PRINT
X
120
LET X=
X +1
130
IF X>=
5 THEN
135
GOTO 1
10
140
END
Run the program and record the output.
Compare the output you recorded above to the output you recorded
after step 1. Is there any connection?
L
5. Display the program in memory. Line 130 of this program is the
assertion X > = 5, which is means "X is greater than or equal to 5”
If, for example, X had the numerical value 6, the assertion would be
true. If X had the value 3, the assertion would be false.
Now look at the program in step 4. If the program is executed,
the computer starts with line 100, then goes to lines 110, 120, and
130. If the assertion in line 130 is true, which line number will the
computer execute next?
106 Hands-on BASIC
6. Only two conditions have been used so far in the programs. They
are
< (Less than)
>= (Greater than or equal to)
How would you write the conditions for
Greater than
L
Less than or equal to
Equal to
L
Not equal to
L
If you can fill in the blanks above without too much trouble, fine.
If not, don't worry. We will review everything later. The important
thing to grasp now is how the IF THEN statement works.
7. Let's explore some applications of the IF THEN statement. Clear the
program in memory and enter the following program:
100 PRINT "INPUT EITHER 1, 2, OR 3 " ;
110 INPUT V
120 IF Y=1 THEN 150
130 IF Y=2 THEN 170
140 IF Y=3 THEN 190
150 PRINT "BLOOD"
160 GOTO 100
170 PRINT "SWEAT"
180 GOTO 100
190 PRINT "TEARS"
2 0 0 G 0 T 0 1 0 0
210 END
Decisions and Branching 107
Display the program and check that you have entered it correctly.
Study the program briefly. Remember that when the computer
executes the program and types out the INPUT prompt, you are
supposed to type in either 1, 2, or 3. Which value of Y will let the
computer reach line 120 in the program?
Which value or values of Y will let the computer reach line 130?
How about line 140?
8. Suppose you wanted the computer to type "SWEAT". What value
of Y should you enter?
i_
See if you were right. Run the program and enter the number you
wrote down. What happened?
9. What value of Y will cause the computer to type BLOOD?
How would you make the computer type TEARS?
Check each of your responses above to see if you were right.
The program assumes that either 1, 2, or 3 will be typed in at the
INPUT prompt. Think about the program a bit, then try to figure
out what will happen if you type 4 in response to the input prompt.
What do you think will happen?
10.
108 Hands-on BASIC
Run the program, type 4 in response to the input prompt, and record
the output.
L
You can easily explain what happened in the program by considering
what the computer does when it encounters an assertion in the IF
THEN statement. Remember, if the assertion is true, the computer
goes to the line number following the THEN. If the condition is false,
the computer goes to the next higher line number. Now jump the
computer out of the INPUT loop.
11. Delete lines 150 through 190 and display the program to make sure
the lines were deleted.
12. Now use another form of the IF THEN statement. Change lines 120,
130, and 140 as follows
120 IF V = 1 THEN PRINT "BLOOD 11
138 IF Y=2 THEN PRINT "SWEAT"
140 IF Y=3 THEN PRINT "TEARS"
Run the program. Is a line number required after the THEN in an
IF THEN statement?
L
13. Now jump the computer out of the input loop and add line 150 as
follows
158 IF Y>3 THEN 210
Display the program. What will happen now if you enter 4 when
you run the program?
Decisions and Branching 109
14. You can control a program with a single keystroke by using the GET
statement. Clear the program in memory and type in the following
program:
80 DIM A$< 1 >
90 OPEN #1,12,0,"K ="
100 PRINT "PRESS A KEY"
110 GET #1,A
120 LET A$=CHR$< A >
130 IF A$="Q" THEN 160
140 PRINT A$
1 5 0 G 0 T 0 10 0
160 PRINT "QUIT"
170 END
Do not be concerned with the statements in lines 80, 90, 110, and
120. They will be covered later. For now, just be careful to type
them in correctly. Try pressing several keys (including the spacebar)
before you press Q. Run the program. What happened?
L
Press Q to stop the program. Is Q printed out by line 130?
15. Now let’s look at a use of the GET statement in a graphics program.
Clear the memory and type the following program.
80 REM POINT MUUING PROGRAM
90 DIM Y$< 1 )
100 OPEN #1,12,0, " K = "
110 GRAPHICS 8
120 LET A =160
130 LET B = 9 6
140 REM PLOTS A WHITE POINT AT
15 0 C 0 L 0 R 1
160 PLOT A,B
170 GET # 1 , X
180 LET Y$=CHR$00
190 REM PLOTS A BLACK POINT AT
2 0 0 C 0 L 0 R 0
210 PLOT A,B
< A, B >
A, B >
110 Hands-on BASIC
220
IF Y$
- » n !!
THEN
B = B + 5
230
IF Y$
_ ii 1 ! i!
THFN
B = B - 5
240
IF Y$
_ il L 11
THEN
H = H-5
250
IF Ys
_ li p !!
THEN
A = h + 5
260
IF Y$
= " f) M
THEN
280
278
L 0 J 0
i cijj
280 END
16. This program allows you to use the U, D, L, and R keys to move a
point around the screen. Run the program and move the point just
off the screen by pressing U a number of times. As it disappears,
you will get an error message. To see what quantity is illegal, in
direct mode type in
P RI N T A, B
Run the program again and move the point to the upper left-hand
corner of the screen being careful not to go off the screen. Move the
point about the screen to get the feel of this program. Type Q to
end the program.
How far does the point move each time you press U, D, L, or
R? (Listing the program in text mode may be helpful.)
L
17. Save this program on a diskette under the name POINT for use at
a later time.
18. Enter text mode. Clear the screen and the memory. Type the
following program.
100 LET 3=0
110 INPUT Y
120 IF ¥=11111 THEN 150
130 LET S=S + ¥
1 4 0 r q j 0 i 0 g
i g g p p j w j S
160 E HD
This program is supposed to add up numbers that are input. The
input value that causes the sum to be printed out is 11111. It is not
part of the sum.
Decisions and Branching 111
19. Run the program and each time the INPUT prompt is displayed, type
in one number from the following sequence of numbers (remember
to press [RETURN! after each number).
11111
What value is printed out for S?
i_
Is this value of S the sum of the numbers you input?
L
20. Let's try to find out why. Type the following line
135 PRINT H S = ";S
List the program. Run the program and input the same values as in
step 19 (3,1,6,5,11111). Compare the values of S in line 135 to the
values input in line 110.
Though you may have already discovered the logical error in the
program, trace the execution of the program by going through the
program as if you were the computer. Do this for the first one or two
input values and then for the last two of the input values. Observe
that the GOTO statement in line 140 goes to the wrong line, that
is, line 100, where S is reset to zero each time.
21. Delete line 135 and retype line 140 as follows
140 GOTO 110
Run the program and input the same values (3,1,6,5,11111). Is the
printout correct this time?
Run the program a final time with different values to verify its
correctness.
112 Hands-on BASIC
22. Turn off the computer and go on to the discussion of the objectives.
6-3 DISCUSSION
Making Transfer Decisions in Programs
In this chapter we are concerned mainly with transfer statements,
both conditional and unconditional, as well as their use in programs.
Before getting to the programming, we will discuss each type of
transfer statement.
a. Unconditional Transfers
From the very beginning of the book, we have been using uncondi¬
tional transfer statements. The following program illustrates the use
of the unconditional transfer statement:
1 0 0
LET Z
— £1
110
PRINT
*7
120
LET Z
=2*
130
G 0 T O
110
140
END
Recall that when ordered to execute a BASIC program, the computer
goes to the statement with the lowest line number and then executes
the statements in increasing line number order. The only way to
interrupt this is with a transfer statement (or, as you will see in
the next chapter, a loop command). In the program above, the
computer would execute line numbers as follows: 100, 110, 120,
130, 110, 120, 130, 110, 120, 130, and so on. The point is that the
statement in line 130 causes the computer to jump back to line 110
instead of going to 140, Note that there are no conditions attached
to the statement in line 130. For this reason the GOTO statement is
known as an unconditional transfer statement. It is also clear that
the GOTO statement in this case puts the program into a loop, and
there is no way out. The only way we can get the computer out of
the loop is to interrupt the program from the keyboard while it is
running.
GOTO is unconditional
Decisions and Branching 113
To sum up, if at some point in a program you want the
computer to make an unconditional jump to another line without
any conditions attached, use the GOTO statement. However, be
careful that you don't get the program "hung up" in a loop.
b. Conditional Transfers
By now you have most likely established the connection between
the IF THEN statements you saw in the discovery exercises and the
notion of the conditional transfer statement. All conditional transfer
statements have the same form. A description of this form and a
sample IF THEN statement are given below:
Line $ IF <relation> <condition> <relation> THEN Line ^
240 IF 3*X-2>Y-Z THEN 360
■ IF THEN statements state conditions.
No matter what the assertion, all IF THEN statements have
this same format. The IF and THEN as well as the two line numbers
in the statement require no special explanation. However, the heart
of the statement lies in the two expressions separated by the condi¬
tion that forms the assertion. We must look at them very carefully.
Several conditions may be used in the IF THEN statement.
The conditions and their meaning are listed below.
Condition
Meaning
=
Equal to
<
Less than
>
Greater than
< =
Less than or equal to
> =
Greater than or equal to
<>
Not equal to
Except for the IF THEN statement above, you have seen only
simple variables and constants in IF THEN statements. This is the
type of assertion used in programs most often. Examples are
100 IF W<3
THEN 250
114 Hands-on BASIC
340 IF S>T THEN 220
There are instances, however, when you might want to use
more complicated expressions in the IF THEN statements. In the
statement
240 IF 3*a-2>Y-Z THEN 360
the first relation is
3*H-2
which is fine providing that X has a value. The second relation,
y_"7
can also be used if Y and Z have values. Suppose that X has the value
1, Y is 10, and Z is 4. The computer will translate the statement
240 IF 3$X-2>V-Z THEN 360
by substituting the values of X, Y, and Z. This changes the statement
to
240 IF 1>6 THEN 360
Sooner or later, all IF THEN statement are reduced to this
form, from which the computer must judge whether an assertion
established by two numbers and a condition is true or false. In this
case, the assertion 1 > 6 is false. However, the assertion 4 < 10
would be true. If the assertion is true, the computer will go to the
line number following THEN. If the assertion is false, the computer
will go to the next higher line number in the program.
■ A true IF THEN statement causes the computer to branch;
a false one causes it to go to the next higher line number.
When the "statement" following the THEN is a number, the
computer will branch to the line with that number if the IF THEN
statement is true. If the statement following the THEN is another
statement, the computer will execute that statement and proceed to
the next line.
With IF THEN (or conditional) transfer statements, you can
make the computer branch anywhere you desire in a program. This
ability gives the computer its great programming potential.
Decisions and Branching 115
6-4 PROGRAM EXAMPLES
Example 1 - Printout of Number Ffctterns
The problem is to write a program that will make the computer print
out the following number pattern:
2 3 4 5
6 7 8 9
10
You must think about several characteristics of this pattern when you
write the program. The first number is 2, and succeeding numbers
are spaced across in the standard manner (four numbers to a line).
Each number is 1 greater than the previous one. The last number is
10, then the computer should stop.
Several solutions are possible. This program, though not
elegant, will work:
100 PRINT 2,3,4,5,6,7,8,9,10
110 END
You might check this program to see that is does in fact produce the
correct number pattern. This program illustrates a very important
concept. There is no such thing as the correct program. The only
test that can be applied is “Does the program work?” Certainly some
programs are cleverer or may accomplish the results more efficiently
than others, but this is a separate issue.
Another way to approach the problem is to make the com¬
puter print the first number in the pattern. You also want to organize
the program so that only a single print statement is required. The
solution is to have the computer print the value of a variable that
will change as it executes the program. You can start the program
with the following segment:
100 LET ft=2
110 PRINT Xj
The value of X is set to 2, and this value is printed out in line
110. The comma causes the computer to space across to the next
standard printing position. Now you must generate the next value
to be printed out. Note that at any point in the pattern, the next
116 Hands-on BASIC
number is just 1 more than the present number. You can generate
the next number with
120 LET X = X+1
Now all that remains is to give the computer a way to make a
decision about whether to loop back to the print statement or to
stop. As long as X is less than or equal to 10, you want to loop
back, so you can use a conditional transfer statement.
130 IF X< = 10 THEN 110
Finish the program with an END statement.
140 END
The complete program is
100 LET X=2
110 PRINT X,
120 LET X = X+1
130 IF X<=10 THEN 110
140 END
This program is simple and has little practical value other than to
illustrate how a conditional transfer statement can get you out of a
program at the proper time.
Example 2 - Automobile License Fees
In an attempt to force consumers to use lower-horsepower cars and
conserve energy, the state adopts a set of progressive annual license
fees based on the power rating of the car. The criteria and fees are
listed below.
Horsepower
License Fee
Up to 50 hp
$0
More than 50 but 100 hp or less
30
More than 100 but 200 hp or less
70
More than 200 but 300 hp or less
150
More than 300 hp
500
Decisions and Branching 117
You want a program that will produce the following output:
INPUT AUTU HP? (You type in horsepower)
LICENSE FEE IS (Computer types out fee)
INPUT AUTO HP? (You type in horsepower)
LICENSE FEE IS (Computer types out fee)
(etc.)
Clearly, the only difficult part of the program will be instructing the
computer to decide what the fee is. The IF THEN statement is made
to order for this decision-making process. To get started, provide
for input of the power rating. Use P to stand for the power rating
of the car. The program can begin with
100 PRINT "INPUT AUTO HP ";
110 INPUT P
Now, you must work out a method to have the computer
decide in which license category P lies. A logical way to do this
would be to check upward from the low horsepower ratings. First,
the computer can check whether P is 50 or less. If so, then the tax
is 0.
120 IF P< =50 THEN _(Fee is 0)
Notice that there is no line number following THEN. If the number
in P is less than or equal to 50, we want the computer to jump to
a statement that will assign the value 0 to the fee. The problem is
that we don't know at this point what line number should be used
for this statement. Consequently, we will leave it blank and insert
the proper value later. The note at the right is a reminder of what
the fee is supposed to be if the assertion is true and the branch is
taken.
If the assertion in line 120 is false, the computer will go to
the next higher line number. The statement in that line should have
the computer test whether P falls in the next higher category.
130 IF P< — 100 THEN _(Fee is $30)
118 Hands-on BASIC
Again, we don't know what line number to use following the THEN
but can fill it in later. We need three further branch statements to
accommodate all categories of P. Now that the pattern is established,
we can include them all at once.
140 if P<=200 THEN _(Fee is $70)
150 IF P< = 300 THEN _(Fee is $150)
160 IF P > 3 0 0 THEN _(Fee is $500)
The program to this point is
100 PRINT 11 INPUT AUTO HP 11 ;
110 INPUT P
120 IF P< =50 THEN _(Fee is 0)
130 IF P< — 100 THEN _(Fee is $30)
140 IF P<=200 THEN _(Fee is $70)
150 IF P<=300 THEN ____^(Fee is $150)
160 IF P>300 THEN ___(Fee is $500)
Now we can fill in the missing line number in line 120. Since
the next line number in the program would be 170, we may as well
use it.
1 0 0
PRINT
"INPUT AUTO
HP
110
INPUT
P
120
IF P<
= 50
THEN 170
130
IF P<
= 110
THEN _
(Fee is $30)
140
IF P<
= 2 0 0
THEN _
(Fee is $70)
150
IF P<
= 3 0 0
THEN _
(Fee is $150)
160
IF P>
300
THEN
_(Fee is $500)
170
LET F
= 0
180
GOTO
_<PRINT
statement >
Again, you don't yet know what line number to use in line
180. Use a reminder because you want the computer to jump to a
PRINT statement after it determines the fee. If the assertion in line
120 is true, the computer jumps to line 170 and assigns the value 0
to F, which stands for the fee. We can fill in the missing numbers in
lines 130, 140, 150, and 160 using the same pattern. The result is
100 PRINT "INPUT AUTO HP
110 INPUT P
H .
Decisions and Branching 119
120 IF P< =50 THEN 170
130 IF F'< = 100 THEN 190
140 IF F'< =200 THEN 210
150 IF P< =300 THEN 230
160 IF P>300 THEN 250
170 LET F=0
180 L UTO _(PR I NT statement)
190 LET F=30
200 GOTO _(PRINT statement)
210 LET F = 70
220 GOTO _(PRINT statement)
230 LET F=150
240 GOTO _(PRINT statement)
250 LET F=500
The next line in the program would be 260, which you may
as well use for the PRINT statement. The rest of the program is
given below.
100 PRINT "INPUT AUTO HP ";
110 INPUT P
120 IF P< =50 THEN 170
130 IF P< = 100 THEN 190
140 IF P<=200 THEN 210
150 IF P<=300 THEN 230
160 IF P>300 THEN 250
170 LET F=0
180 GOTO 260
190 LET F = 30
200 G0TO 260
210 LET F = 70
220 GOTO 260
230 LET F =150
2 4 0 G 0 T 0 2 6 0
250 LET F=500
260 PRINT "LICENSE FEE IS " i F
270 PRINT
280 GOTO 100
290 END
You may have noticed that the conditional transfer statement
in line 160 is not necessary. To see why, consider each of the
120 Hands-on BASIC
assertions in the IF THEN statements. If the assertion in line 120 is
false, P must be greater than 50. Likewise, if each of the following
assertions is false, the computer goes to the next higher line number.
Suppose the computer reaches line 150 and determines that the
assertion is false. This directs the computer to line 160, but that
jump is unnecessary. You already know that P must be greater than
300, and the computer can therefore print out the fee without any
more testing. If you assign the license fee of $500 in line 160, you
use a slightly different program:
1 0 0
PRINT
“ INP
UT Hi
JT
0
110
INPUT
P
120
IF P<
=50 THEN 20
0
130
IF P<
= 1 0 0
THEN
2
20
140
IF P<
= 2 0 0
THEN
cL
40
150
IF P<
= 300
THEN
60
160
LET F
= 5 0 0
170
PRINT
" L I C
ENSE
P
EE
180
PRINT
190
G 0 T 0
1 0 0
2 0 0
LET F
= 0
210
G 0 T 0
170
2 2 0
LET F
= 30
230
G 0 T 0
1 70
240
LET F
= 70
250
G 0 T 0
1 70
260
LET F
= 150
270
G 0 T 0
1 7 Cl
2 8 0
END
Yet another solution for this problem is listed below. Study it
to make certain you understand how it works.
100 PRINT 11 INPUT AUTO HP ” ;
110 INPUT P
120 IF p>308 THEN F=500
130 IF P<=300 THEN F-150
140 if p < = 200 THEN! F=70
150 IF PO100 THEN F=30
160 IF P< =50 THEN F = 0
170 PRINT "LICENSE FEE IS "; F
130 PRINT
Decisions and Branching 121
130 LUT0 100
200 END
All three versions of the program will work equally well, and
you may have your own version. You can decide how you prefer to
handle the branches. The main question is whether your program
will work.
We have gone through this program in great detail because
beginners often have difficulty writing programs that use transfer
statements. You should study the program until you are convinced
that it does accomplish what is desired. Remember to leave line
numbers out when you do not know what they should be, then
return later to fill in the proper numbers. Also, use comments at the
right of each line that refers to an as yet undetermnind line number.
Those comments will help you remember what you want to happen
at that branch point in the program. In fact, consider using these
comments any time you use an IF THEN statement. When you reread
an old program, these comments remind you of what the program
is supposed to accomplish.
Example 3 - Averaging Numbers
Suppose you wish to average the numbers in a DATA statement.
The problem is that you don’t know in advance how many numbers
there are. So you will use a flag variable to mark the end of the
data. The flag will be a number that is very unlikely to occur in the
data. We will use the number 9999 as the flag here, but you could
select any unlikely number.
Here is the way it will work. The DATA statement will always
appear as follows:
Line # DATA (number),(number),....,(number ),9999
Place the flag 9999 after the last number to be averaged. Each
time the computer reads a number from the DATA statement in the
program, it checks to see if it is 9999. If not, the computer reads the
number as part of the data to be averaged. If the number is 9999
the computer goes on to the rest of the program.
An average is computed by dividing the sum of the numbers
by the number of numbers. The program must give the computer a
way to ascertain both these quantities. Use S to stand for the sum of
122 Hands-on BASIC
the numbers and N for the number of numbers. When the program
is executed, you do not know what these values will be, so set them
equal to 0. The computer will then develop their values as it reads
numbers from the DATA statements.
Begin the program by setting up the initial values of S and N.
100 LET S=0
110 LET N=0
Next you can program the computer to read a number from
the DATA statement and check for the flag value.
120 READ X
130 IF X = 3999 THEN _(Compute average)
Use the method introduced in the previous example of leaving
a blank line number in the conditional transfer statement until you
know what that line number should be. In this case, if the assertion
X = 9999 is true, then the computer is signaled that all the numbers
in the DATA statement have been processed and that it can now
compute the average. If the assertion is false, the computer reads
the number as part of the data and processes that number as follows:
140 LET S=S + X
150 LET N=N+1
In line 140, the value of X (the number just read) is added
to the value in S. Remember that the sum of all the numbers to
be averaged is being developed in S. In line 150, the number in N
is increased by 1 to record the fact that another number has been
processed. You are now ready to program the computer to process
the next number. This statement does the job.
160 GOTO 120
Now you can fill in the missing number in line 130, since the
next line number in the program would normally be 170. Line 170
is an instruction to compute the average, which you can identify by
A. If a typical DATA statement is included, the complete program
is
Decisions and Branching 123
100
LET S — 0
110
LET N = 0
120
READ K
130
IF K=SS3S
140
LET S=S+X
150
LET N=N +1
160
GOTO 120
170
LET A=S s N
180
PRINT A
190
DATA 4,2,
2 0 0
END
Of course, you can have as many DATA statments as needed
to accommodate the numbers to be averaged. Following the last
number in the last DATA statement we put the flag 9999 to mark
the end of the data. This gets the computer out of the READ loop
and signals it to compute the average.
The conditional transfer statement, coupled with the flag vari¬
able, is a powerful programming tool.
6-5 FINDING ERRORS IN PROGRAMS
The ability to look at a program and determine whether it will ac¬
complish what it is supposed to is certainly one of the most im¬
portant skills a beginner can acquire. Probably more to the point,
programmers need the ability to find out what is wrong and correct
it when a program is not working as it should. Although the task
seems difficult, it is really easy.
Two separate skills are involved in troubleshooting programs.
First, you need to decide which variables you would like to see
additional information about. You can insert PRINT statements into
the program to get the computer to print the values of the variables
you want to see. Second, you need to be able to follow the logic of
the program by going through the program as the computer would
(using pencil and paper, if necessary). For loops, it is generally
sufficient to check the first couple of values and the last couple
of values. These two abilities together allow you to find logical
programming errors quickly.
124 Hands-on BASIC
6-6 PROBLEMS
1. Write a BASIC program that calls for the input of two numbers and
prints out the larger.
2. Program a computer to read three numbers from a DATA statement
and then print out the smallest.
3. Write a program that has the computer find and print out the sum
of all the whole numbers between 1 and 100, inclusive.
4. What will happen if you run the following program?
100 LET S=0
110 LET X=1
120 LET S=S + X
130 LET X=X + 2
140 IF X<100 THEN 120 150 PRINT S
160 END
5. In example 3 in this chapter, change line 190 as follows:
190 DATA 4,2,3,6,5,1111
Study the program with this change and write down what will be
output if the program is executed. You may wish to run the program
to see if you are correct. If the answer is not correct, it may be
helpful to insert line 155 as follows:
155 PRINT 11 S= " ;S
List the program before you run it again. Compare the values of
X in the DATA statement with the values of S printed out. If you
can figure out why S = 1131 in the last output, you will know the
reason for the error. If not, try tracing the logic of the program by
doing exactly what the computer would do.
6. Program a computer to find the average of all the positive numbers
in a list whose end is marked with the flag 999. You do not know
in advance what numbers will be part of the data; they will be typed
into the computer when the program is run.
Decisions and Branching 125
7. Suppose you are given a DATA statement that contains a list of
numbers of unknown length. However, the end of the list is marked
with the flag variable 9999. Write a BASIC program to compute
and print out the sum of the numbers in the list between —10 and
+ 10 inclusive.
8. Usually the markup of supermarket items depends on the unit cost
of the item. Suppose this markup is based on the following schedule:
Unit Cost
Mark up
0 to $1.00
20%
$1.01 to $2.00
10%
over $2.00
5%
The unit cost is determined by dividing the case price by the number
of items in the case. Write a program to compute label price, which
is unit cost plus markup.
9. Suppose you agree to work for one cent the first day, two cents the
second, four cents the third, eight cents the fourth and so on. If
there are 22 working days in a month, write a program that will
compute your wages (in dollars) for one month.
10. Consider the series
1 + 1/2 + 1/3 + 1/4 + ...
Write a program to find the sum of the first N terms. Use this to
find the sum of the first 10, 100, and 1000 terms. What do you
think will happen if you let the series run on forever?
11. Study the following program. Can you describe what the program
does?
100 READ N
110 LET L=1
120 LET C=1
130 READ X
140 LET C=C +1
150 IF X<L THEN
160 LET L=X
170 IF C<N THEN
170
130
126 Hands-on BASIC
188 PRINT L
190 DATA 10
200 DATA 5.« 83.« 17.. 3.. 47
210 DATA 25.* 16 .* 41 .* 51 .* 7
220 END
You can find out more about on how the program works by inserting
line 165 as follows
165 PRINT "L IS ”; L
and running the program.
12. The following program is intended to find the average of N numbers
typed in at the terminal. As it stands the program is incorrect.
What's wrong?
1 0 0
PRINT
"HOW
MANY NUMBERS"
110
INPUT
N
120
LET S=
0
130
LET C=
1
140
PRINT
"TYPE
IN A
NUMBER"
150
INPUT
y
160
LET S =
S + X
170
LET C=
C+l
180
IF C<N
THEN
140
196
LET H =
S-'N
2 0 0
PRINT
"THE
AUERAG
:E IS"; A
210
END
13. The discounted price of an item can be computed by
D = L*(l - R/100)
where L is the purchase price and R is the discount rate in percent.
Write a program that will produce the following output:
LIST PR I CE ( $ >? (You type in price)
DISCOUNT RATE < Y? (You type in rate)
DISCOUNTED PRICE IS
(Computer types out price) DOLLARS
Decisions and Branching 127
14. There is an interesting sequence of numbers called the Fibonacci
numbers. The set begins with 0, 1. Then each succeeding number
in the sequence is the sum of the two previous ones. Thus, the
Fibonacci sequence is
0, 1, 1, 2, 3, 5, 8,....
Write a BASIC program to compute and print out the first twenty
numbers in the Fibonacci sequence.
15. Write a program to accept the input of two numbers. If both the
numbers are greater than or equal to 10, print out their sum. If both
the numbers are less than 10, print out their product. If one number
is greater than or equal to 10 and the other is less than 10, print out
the difference between the largest and smallest.
16. An instructor decides to award letter grades on an examination as
follows:
90-100 A
80-89 B
60-79 C
50-59 D
0-50 F
Write a program to produce the following output:
INPUT EXAM GRADE ?(You type in numerical grade)
YOUR GRADE IS (Computer types out A, B, C, D, E, or F)
17. If you use 8 percent more electricity each year, in nine years your
consumption will double. Thus your doubling time is nine years.
There is an interesting rule called the “rule of seventy- two" that
can be used to compute doubling times. If a quantity grows by R
percent in a single period of time, then the number of periods for the
quantity to double is given approximately by 72/R. We can compute
the growth of a process directly on the computer. In a single growth
period, a quantity Q grows according to the relation
Qnev = Qold(l+R/l00)
128 Hands-on BASIC
Thus we can keep track of the growth by repeated use of the relation
above. When Q is twice the original value, the corresponding num¬
ber of growth periods is the doubling time. Using this approach,
write a program that will produce the following output:
GROWTH RATE < X > ? (You type in R)
NUMBER OF GROWTH PERIODS TO DOUBLE IS
(Computer types answer)
Use the program to check out the accuracy of the rule of seventy-two
for many different growth rates.
18. A set of integers (whole numbers) is chosen at random from the set
1, 2, 3, 4 and put in a DATA statement. The end of the set is marked
with the flag 9999. Write a BASIC program that will compute and
print out the number of Is, 2s, 3s, and 4s in the set. Test your
program on the following DATA statement:
DATA 3 .* 1 .> 2 .» 1 .. 4 .. 4 .. 1 .» 2 .« 2 .« 2 .» 3 .« 3 3 3 3
19. Write a program that draws short lines (10 units) to the left, right,
up, or down depending on which of the keys L, R, U, or D is pressed.
You should model your program after the program in step 15 of the
discovery exercises. Be sure to delete lines 190 through 210 in that
program since they draw lines in the background color. You will
need a DRAWTO statement at the appropriate place. Try running
the program to see how the program draws various lines and figures.
6-7 PRACTICE TEST
1. What will be output if you run the following program?
100 LET V = 3
110 LET H = 2*Y
120 PRINT X
130 LET Y = Y + 2
140 IF Y< = 10 THEN 110
150 END
Decisions and Branching 129
2. What will be output if you run the following program?
1 0 0
READ K
110
DATA 1
j "7
120
IF K<2
THEN 160
130
IF * = 2
THEN 150
140
PRINT
"GOOD"
150
PRINT
"BETTER"
160
PRINT
"BEST"
170
PRINT
180
G 0 T 0 1 0 0
198
END
3. Suppose you decide to buy a number of widgets. The manufacturer
is pushing sales and will reduce prices if widgets are purchased in
quantity. The price reductions are given below:
^Purchased Price per Widget
20 or less
$2.00
21 to 50
1.80
51 or more
1.50
Write a program that will produce the following output when ex¬
ecuted:
HOW MANY WIDGETS ? (You type in purchase quantity)
PRICE PER WIDGET IS (Computer types out unit price)
TOTAL COST OF ORDER IS (Computer types out total)
Then keep looping back through the program.
4. Write a program that will print out the number pattern shown below
and then stop.
0 5 10
15 20 25
etc.
165 170 175
130 Hands-on BASIC
If you get a ticket for speeding, your fine is based on how much you
exceeded the speed limit. Suppose the fine is computed as follows:
Amount over Limit Fine
1-10 mi/h
$ 5
11-20
10
21-30
20
31-40
40
41 or more
80
Write a BASIC program that will produce the following output:
WHAT WAS THE SPEED LIMIT ? (You type in)
SPEED ARRESTED AT ? (You type in)
FINE IS (Computer types out fine) DOLLARS
CHAPTER 7
LOOPING AND
FUNCTIONS
7-1 OBJECTIVES
Using Built-in Looping Statements
You have already learned how to loop programs using either the
unconditional or conditional transfer statements. Now you will
learn special BASIC statements that take care of looping automati¬
cally. These statements simplify the programming task and provide
flexibility in programs.
Using Built-in Functions
BASIC contains a number of built-in functions that can be used to
perform specific tasks. You will learn to use some of the simpler of
these functions involving numerical computations.
Working with Program Examples
You will continue with activities designed to draw you into program¬
ming. Remember that the overall objective of the book is to teach
you how to write BASIC language programs.
132 Hands-on BASIC
7-2 DISCOVERY EXERCISES
1. Turn on the computer, bring up ATARI BASIC, and enter the fol¬
lowing program:
100 LET Y=10
110 PRINT Y,
120 LET Y=Y+5
130 IF Y<=50 THEN 110
140 END
Study the program and then execute it. Record what happened.
Which statement in the program determines the difference in the
numbers that were typed out?
2. Clear out the program in memory and enter the following program:
100 FOR Y =10 TO 50 STEP 5
110 PRINT Y,
120 NEXT Y
130 END
Run the program and record what happened.
Compare the output to that obtained from the program in step 1.
3. Since the two programs produce the same output, it is reasonable to
assume that the statements must be related in some way. Type
100 FOR ¥=10 TO 50 STEP 10
Display the program in memory and study it. What do you think
will happen if you run this program?
Looping and Functions 133
See if you were right. Run the program and record the results.
i_
4. Now try out a few different ideas. Type
100 FOR Y = 0 TO 5 STEP 1
Display the program. What do you think this program will do?
i_
Run the program and record the output.
i_
5. Now type
100 FOR Y=0 TO 5
Display the program. What do you think this program will do?
i_
Run the program and record the output.
i_
Now compare line 100 in the program just executed with line 100
in the program in step 4. If the difference between the numbers to
be printed out is 1, is the STEP part of the statement necessary?
i_
6. Let ; s try a different tactic. Type
100 FOR Y=20 TO 10 STEP -2
Display the program and study it. What do you think this program
will do?
134 Hands-on BASIC
Run the program and record the output.
7. Now type
100 FOR Y=10 TO 20 STEP -2
Display the program. What do you think will happen now if you
run the program?
Run the program and record the output.
We have led you into a potential trap in BASIC. What seems to be
the problem?
8. So far the step sizes in the FOR NEXT statements have worked out
even. Let's try a new step size that might not come out even given
the limits in the FOR NEXT statement. Type
100 FOR Y=2 TO 3 STEP 3
Display the program. What do you think will be printed out?
Run the program and record the output.
Looping and Functions 1 35
9. Clear the program in memory and enter the following program:
100 FOR X=1 TO 3
110 FOR Y=1 TO 4
120 PRINT X.« Y
130 NEXT Y
140 NEXT X
150 END
Run the program and record the output.
10. Now type
100 FOR X=1 TO 2
Run this new program and record the output.
Compare the two number patterns you have obtained. Can you see
the connection between the patterns and the limits in the FOR NEXT
statements?
11. Let ; s modify the program a bit more. Type
100 FOR X=1 TO 3
110 FOR r = 1 TO 2
Display this program and study it. What do you think will be the
output if you run it?
Try it and see if you were right.
136 Hands-on BASIC
12. Type
100 FOR X=1 TO 2
110 FOR Y =1 TO 2
Display the program and write down what you think will be typed
out when you run the program.
Run the program and record the results.
Obtain a listing of the program just executed and draw a line from
the line number of the FOR Y statement to the line number of the
NEXT Y statement. Do the same thing for the FOR X and the NEXT
X statements. Do the lines cross?
13. Now type
100 FOR Y =1 TO 2
110 FOR X=1 TO 2
Display the program. What do you think will be output of this
program?
L
Run the program and record the output.
i_
Obtain a listing of this program. Connect the FOR Y and the NEXT
Y line numbers with a line just as you did in step 12. Do the same
thing for the FOR X and the NEXT X statements. Do the lines cross?
Compare with the situation in step 12.
Looping and Functions 137
Does this suggest a way to avoid getting into trouble using more
than one FOR NEXT combination in a single program?
14. Clear the program in memory. Enter the program below.
100 GRAPHICS 8
110 FOR 1=1 TO 150 STEP 5
120 FOR J=1 TO 0 STEP -1
130 C 0L 0R J
140 PLOT 1,1:DRAWTO 1+20,I
150 DRAWTO 1+20,1+20
160 DRAWTO I , I+20 = DRAWTO I, I
170 NEXT J
180 NEXT I
130 END
Study the program. What shape do you think will be drawn by lines
140 to 160?
Run the program. Were you right?
L
What two colors are used in this program?
i_
15. Exit the graphics mode by typing GRAPHICS 0 Clear the program
in memory and enter the program below.
100 INPUT A
110 LET B=SQR< A >
120 PRINT B
1 3 0 G 0 T 0 1 0 0
140 END
Run the program and at the INPUT prompt, type in 4. What
happened?
138 Hands-on BASIC
Type in 9 at the INPUT prompt and record the results.
L
Type in 25. What happened?
Finally, type in 10. What happened?
What happens to A in the expression SQR(A) in line 110 of the
program? In other words, what does SQR do?
16. Jump the computer out of the input loop. Type
110 LET B=INT< A >
Run the program for the following values of A. In each case, record
the output of the program.
A Output
1 _
3.4 _
256.78 _
0 _
~1 __
-2.3 _
Examine the output you have recorded above and compare each
number with the corresponding value of A that you typed in. What
does the INT(A) function do?
Looping and Functions 139
If you had trouble understanding what was happening to the nega¬
tive values of A, don't worry at this point. We will review this
completely later.
17. Jump the computer out of the input loop. Type
110 LET B = SGN<A >
Display the program and review the program structure to refresh
your memory about how the program works. Run the program for
each of the following values of A. In each case, record the output.
A Output
1.5
43 _
128.3 _
0 _
-1 _
- 1.2 _
-345.7 _
4.7 _
-5.8 _
Examine the output carefully. What does the SGN function do?
18. Jump the computer out of the input loop. Type
110 LET B=ABS<ft >
Execute the program for each of the values of A given below. Again,
record the output in each case.
140
Hands-on BASIC
A Output
3.4 _
0 _
-3.4 _
-2 _
-8.45 _
8.45 _
Examine the output. What does the ABS function do?
I_
19. This concludes the computer work for now. Jump the computer out
of the input loop and turn off the computer.
7 — 3 DISCUSSION
Using Built-in Looping Statements
In the previous chapters you learned how to loop programs under the
control of transfer statements. The unconditional (GOTO) statement
was useful but could sometimes result in a loop with no way out.
The conditional (IF THEN) statement provided a way to loop the
program and also a way to get out of the loop. All of these are
good techniques. However, BASIC gives programmers a simple and
elegant way to take care of looping. We will now go over this new
method, which uses the FOR NEXT statements.
All FOR statements have the same format. This format and a
typical statement are shown below.
Line# F0R<variable> = <relation>TO<relation> STEP<relation>
120 FOR X=1 TO 9 STEP 2
The things that can change in FOR statements are the variable and
the three relations. If the STEP is left out of the statement, the
Looping and Functions 141
computer will use a step size of 1. There are many different forms
of the FOR statement. A few of the possibilities are:
FOR J=2 TO 8
FOR T=25 TO 10 STEP -2
FOR W=-28 TO 10 STEP 2
FOR 3=3*2 TO A*B STEP 0
In general, you can use any legal BASIC statement for the
relations if the variables are properly defined in the program.
■ Use FOR NEXT statements for looping.
The FOR statement opens a loop. You close the loop with the
NEXT statement. The following example shows how this is done.
200 FOR 3=2 TO 18 STEP 2 (Opens loop)
130
130
130
130
Program lines inside loop
340 NEXT 3 (Closes loop)
In the NEXT statement, the variable must be the same as that in the
FOR statement that opened the loop.
It is important to acquire a complete understanding of how
these loops work. In the example above, when the program reaches
line 200 the first time, X is set equal to 2. Then the computer works
through the lines until it reaches line 340, which closes the loop and
directs the computer back to line 200 and the next value of X (in this
case, 4). The computer stays in the loop until the value of X exceeds
the limit of 18. Then, instead of going through the statements inside
the loop, the computer jumps to the line following line 340.
142 Hands-on BASIC
Let’s look at another example of the FOR NEXT statements in
action.
100 LET A= 1
110 FOR X =1 TO 6 STEP 2
120 LET A=2*A
130 PRINT A, X
140 NEXT X
150 END
The table below shows the line numbers in the order the
computer encounters them and gives the corresponding values of the
variables at each stage.
Line Number A X
100
1
110
1
1
120
2
1
130
2
1
140
2
1
110
2
3
120
4
3
130
4
3
140
4
3
110
4
5
120
8
5
130
8
5
140
8
5
110
8
7*
150
**
* Jumps out of loop
** Program stops
Study the sequence of line numbers and the corresponding
values of A and X until you are certain that you understand how the
FOR NEXT statements control the loop.
Quite often a program requires more complicated loop struc¬
tures. The structure can be as involved as desired provided that the
loops do not cross. The example below illustrates a segment of a
program with crossed loops.
Looping and Functions 143
100 FOR A=2 TO 20
110 FOR B=4 TO 8
Loops cross!
240 NEXT A
250 NEXT B
Another example of crossed loops is
100 FOR 1=0 TO 20 STEP 2
110 FOR A=10 TO 2 STEP -1
120 FOR B=1 TO 4
Outer loop OK; inner loops cross!
170 NEXT A
180 NEXT B
190 NEXT I
With large complex programs containing many FOR NEXT
loops, it is easy to cross one or more of the loops. However, when
this does happen, the error message will point you quickly to it.
The following example illustrates a complicated structure in
which the loops are organized correctly:
I 0 0
FOR
X = 1
TO 10
110
FOR
Y=2
TO 4
1 40
NEX
T Y
170
FOR
Z=1
TO 5
210
FOR
K = 2
0 T 0 10
270
NEX
T K
31 0
NEX
T Z
STEP -2
144 Hands-on BASIC
In this example we have double loops and loops within loops.
Remember, any combination of loops may be used in a program
provided that lines connecting the FOR statements and their cor¬
responding NEXT statements do not cross. If they do, the computer
will signal an error and stop.
■ Don't cross your FOR NEXT loops!
Using Built— in Functions
Since many computing tasks are needed routinely, ATARI BASIC
has some tasks preprogrammed in the form of functions. With these
built-in functions, the programmer can perform very complicated
mathematical operations without difficulty. The functions include
the following:
Function
Action
SQR(X)
Square root of X
INT(X)
Integer part of X
SGN(X)
Sign of X
ABS(X)
Absolute value of X
Let's examine the first function, SQR(X), to see how all the
functions operate in general. First, X is called the argument of the
function and can be thought of as "what the function works on." If
you use SQR(X) in a program, you are instructing the computer to
look up the value of X and take the square root of that number. For
example.
SQR(36) =
6
SQR(64) =
8
SQR(81) =
9
SQR(2) =
1.41421356
and so on. The only limitation is that you can't take the square
root of a negative number. If you asked the computer to evaluate
SQR( 6), for example, it would signal an error and stop.
Looping and Functions 145
The argument of the function can be as complicated as needed
in the program. If the computer runs across an expression such as
SQR(X + 4*Y)
it will look up the values of the variables, carry out the calculation
indicated, and take the square root of the result. This characteristic
is true for all the functions.
INT(X) takes the integer part of X. The term integer means
''whole number." Thus, 2 is an integer while 23.472 is not. To take
the integer part of a number, you simply forget about everything
following the decimal point. Thus
INT(3.1593) = 3
INT(54.76) = 54
1NT(0.362) = 0
However, negative numbers require special attention. What really
happens when you take the integer of a number is that you go to
the first integer less than or equal to the number. Using this rule,
INT(—2) - -2
INT(-.93) = -1
and so on. Note carefully that the INT function does not round off
a number. Often beginners are somewhat confused about this.
■ The integer part of a number is the first integer
less than the number.
SGN(X) is a very interesting function. If X is positive, SGN(X)
is +1. If X is negative, SGN(X) is —1. If X is 0, SGN(X) is 0. In
effect, SGN(X) returns the sign of X, either +1, —1, or 0. Therefore,
SGN(4.568) = +1
SGN(375) = +1
SGN(O) = 0
SGN(—5.93) = -1
SGN(—4) = -1
146 Hands-on BASIC
At this point it may not be clear how such a function could
be useful. The SGN function is very useful, however, and has many
applications. For the time being, it is enough simply to learn what
the function does.
ABS(X) tells the computer to ignore the sign of X. In effect,
it converts all values of X, other than 0, to positive numbers. For
example:
ABS(4.5) = 4.5
ABS(—4.5) = 4.5
ABS(95.34) = 95.34
ABS(—95.34) = 95.34
ABS(O) = 0
There are many other built-in functions in BASIC. Fiowever,
most of them involve more mathematical knowledge than many
students have. If you know the mathematics necessary to understand
what the functions are doing, you will have no difficulty learning
how to use them. If you are interested, consult Chapter 6 of the
ATARI BASIC Reference Manual. We will take up some functions
that involve strings of characters in Chapter 9.
The built-in functions we have been discussing are used in
BASIC statements. Lines that use such functions might include
100 LET X = SQR< V )
100 LET Z= 3 #INT<C >+ABS< D>
The built-in functions can also be used within the argument of
functions such as
100 LET Y = INT<SQR<X>+3*ABS< Z > >
In this example, the computer would add the square root of X to
the absolute value of Z multiplied by 3 and express the sum as an
integer.
■ Any BASIC expression can be the argument of BASIC function
Looping and Functions 147
7-4 PROGRAM EXAMPLES
Example 1 - Finding the Average of a Group of Numbers
In the previous chapter, you found an average in one of the program
examples. Let's return to the same problem but use a different
method. We want the program to produce the following printout:
HOW MANY NUMBERS (You type in)
ENTER NUMBERS, ONE AT A TIME
? (You type in the numbers)
THE AUER AGE IS (Computer types out average)
The first few lines should be easy for you to write by now.
100 PRINT "HOW MANY NUMBERS";
110 INPUT N
120 PRINT "ENTER NUMBERS, ONE AT A TIME"
Now you must arrange for the input of N numbers but must
also keep in mind that we are supposed to compute the average
of the numbers. So initially set S (which will be used to sum the
numbers) equal to 0.
130 LET S=0
FOR NEXT statements are ideal for inputting numbers and
summing them.
140 FOR 1=1 TO N
150 INPUT X
160 LET 3=S+X
170 NEXT I
You don't use I, the loop variable, except to count the numbers as
they are input. When all the numbers are in, the computer will
jump out of the loop to the next line after 170. When this happens,
S will contain the sum of all the values of X that were typed in.
Since you know that N is the number of numbers typed in, you can
immediately get the program to compute the average.
180 LET A=S***N
The rest of the program follows without difficulty.
148 Hands-on BASIC
190 PRINT “THE hUERhGE IS " ; h
208 END
The complete program is
1 00
PRINT
"HOW
MANY NUMBER
C 11
110
INPUT
N
120
PRINT
"ENTER NUMBERS,
ONE
130
LET S=
0
140
FOR 1 =
1 TO
N
150
INPUT
160
LET S=
s+x
170
NEXT I
180
LET A =
S/N
190
PRINT
"THE
AVERAGE IS
" A
2 0 0
END
Example 2 - Temperature Conversion Table
In one of the earlier programs you used the relation
C = 5/9*(F —32)
to convert from degrees Fahrenheit to degrees Celsius. Now let's
generate a conversion table as follows:
Degrees F Degrees C
0
-17.77777777
5
-15
10
-12.22222222
etc.
100
3 7.77777777
First you'll want the column headings and a space before the
table begins.
100 PRINT "DEGREES F","DEGREES C"
110 PRINT
You can use a FOR NEXT loop to generate the values of F, which
can then be converted to C and printed out.
Looping and Functions 149
120 FOR F=0 TO 100 STEP 5
130 LET C=5*<F-32>/9
140 PRINT F,C
150 NEXT F
Finally you need the END statement.
160 END
The whole program is
100 PRINT "DEGREES F", "DEGREES C
110 PRINT
120 FOR F=0 TO 100 STEP 5
130 LET C=5*<F-32V9
140 PRINT F,C
150 NEXT F
160 END
Example 3 - Exact Division
Now let's write a program that will compute all the integers (whole
numbers) that divide exactly into another integer. To illustrate,
suppose we take N as the test integer. The problem is to find all
the integers (X) that will divide exactly into N with no remainder.
The rule to use is
If N/X = INT(N/X) then there is no remainder
If N/X <> INT(N/X) then there is a remainder
Now write a program to produce the following output when
executed:
IN PUT h P 0S I TI U E W HOLE NIJ MBE R? (You type in)
THE EXACT DIUISORS ARE
(Computer types out first number, second number, etc.)
150 Hands-on BASIC
The program begins easily.
100 PRINT "INPUT A POSITIUE WHOLE NUMBER" i
110 INPUT N
120 PRINT "THE EXACT DIUISORS ARE"
Now you want the program to look at each of the whole
numbers between 1 and N. Of course, this is an ideal use of the FOR
NEXT loop. The rule given above tests whether each number divides
exactly.
130 FOR X=1 TO N
140 IF NX< >INT< N s X > THEN 160
150 PRINT X,
160 NEXT X
Finally you need the END statement.
170 END
The complete program is
100 PRINT "INPUT A POSITIVE WHOLE NUMBER "
110 INPUT N
120 PRINT "THE EXACT DIUISORS ARE"
130 FOR X=1 TO N
140 IF N/XOINKN/K) THEN 160
150 PRINT X,
160 NEXT X
170 END
Try the program using fairly large values of N. How could
you make the program run in half the time?
Example 4 - Depreciation Schedule
When a company invests in equipment, the investment is depreciated
over a number of years for tax purposes. This means that the value
of the equipment decreases each year and the amount of decrease
is a tax-deductible item. One of the methods used to compute
depreciation is the “sum-of-the-years’-digits” schedule.
Looping and Functions 151
To illustrate, suppose a piece of equipment has a lifetime of 5
years. The sum of the years' digits would be
1+2 + 3 + 4+ 5 = 15
The depredation the first year will be 5/15 of the initial value. The
depreciation fraction the second year will be 4/15, and so on. If the
equipment had an initial value of $3000, the depreciation schedule
would be
End of Year
Depreciation
Fraction
Depreciation
Current
Value
1
5/15
1000
2000
2
4/15
800
1200
3
3/15
600
600
4
2/15
400
200
5
1/15
200
0
The problem is to write a BASIC program that will generate
depreciation schedules by the “sum-of-the-years'-digits” method.
The output should be as follows:
THE INITIAL ASSET UAL HE IS (You type in)
THE ASSET LIFE IN VEARS IS (You type in)
END OF DEPREC DEPREC CURRENT
YEAR FRACTION ASSET UALUE
(Computer prints out table)
The first few lines of the program can be written without any
explanation:
100 PRINT "THE INITIAL ASSET UALUE IS
110 INPUT P
120 PRINT "THE ASSET LIFE IN YEARS IS
130 INPUT N
140 PRINT
1 50 PR I NT "END OF " ; " " ; " DEPREC " .; "
" .: " DEPREC " i " " .; " CURRENT "
160 PR I NT " YEAR " ; " " " FRACT I ON " .; "
"ASSET UALUE"
170 PRINT
li .
II .
152 Hands-on BASIC
Next, compute the sum-of-the-years’ digits.
130 LET 3=0
190 FOR 1=1 TO N
200 LET 3=3+1
210 NEXT I
Now compute the schedule and print it out. Use the variable
PI to keep track of the current asset value.
220 LET P1=P
230 FOR 1=1 TO N
240 LET F=< N + l-IVS
250 LET D=P*F
260 LET P1=P1-D
270 PRINT I,F,D,F'l
280 NEXT I
In line 240, F is the depreciation fraction for the Ith year.
You can check this out for various values of I to ensure that the
expression does generate the correct value of F. In line 250, D is the
depreciation. The only thing missing now is the END statement.
290 END
The complete program is
100 PRINT "THE INITIAL ASSET UALUE IS "
110 INPUT P
120 PRINT "THE ASSET LIFE IN YEARS IS "
130 INPUT N
140 PRINT
1 50 PR I NT "END OF " ; " DEPREC " "
" " D E P R E C " " CIJ R R E N T "
1 60 PR I NT " YEAR " .; " " .; " FRACTI ON " "
ASSET UALUE"
170 PRINT
130 LET S=0
190 FOR 1=1 TO N
200 LET 3=3+1
210 NEXT I
220 LET P1= P
Looping and Functions 153
230 FOR 1=1 TO N
240 LET F=<N+1-I>/S
250 LET D=P*F
260 LET P1=P1-D
270 PRINT I,F,D,P1
280 NEXT I
230 END
Try out the program with different inputs. Use $1000 and 4
years first. Other choices will generally give long fractional values
that will wrap around on the screen and be difficult to read. You
can make the table more legible by reducing the number of digits
displayed. See example 2, Chapter 10. You may be able to come
up with a solution yourself using the INT function covered in this
chapter.
Use this program to impress the Internal Revenue Service with
computer-generated depreciation schedules!
7-5 PROBLEMS
1. Write a program to generate a table of numbers and their square
roots. The table should look like the following:
N SQRO-O
1.41421356
1.44913767
1.48323963
etc.
3.9 1.97484176
4 2
2. Write a program to count from 0 to 500 by tens and print out the
results.
3. Write a program to accept the input of a number N, then print out
the even numbers greater than 0 but less than or equal to N.
4. Write a program to print out a conversion table from inches to
centimeters. Include the appropriate headings. Start the table at
0 and continue to 10 inches in steps of 0.5 inch. There are 2.54
centimeters in one inch.
154 Hands-on BASIC
5. What will be printed out if you run the following program?
100 FOR X = 5 TO 1 STEP -1
110 PRINT "ABCD"
120 NEXT X
130 END
6. Study the following program. What will be output?
100 FOR 1=1 TO 5
110 READ A
120 LET B=INTC A >-SGN<A)*2
130 PRINT B
140 NEXT I
150 DATA 2.2,-3,10,0,-1.5
160 END
7. What will be printed out if you run the following program?
1 0 0
FOR X =1 TO
10
120
LET V = 2$X
130
FOR Z=1 TO
cr
140
LET U=Z+Y
150
FOR 0=1 TO
"7
160
PRINT U + iJ
170
NEXT Z
180
NEXT U
190
NEXT X
2 0 0
END
8. The following program won’t work. What’s wrong?
100 FOR X=-10 TO +10 STEP 2
110 PRINT X, SQROO
120 NEXT X
130 END
Looping and Functions 155
9. What does the following program do?
108 FOR X=1 TO 5
HO READ Y
120 LET Z= I NT< 100T.Y+ . 5 '}/ 100
130 PRINT Z
140 NEXT X
150 DATA 1.0 6 1 4 2 .■ 2 7.5 2 9 £ .- 1 3 8.0 21
1 fa 0 DATA .423715.. 51.9132
170 END
10. Write a program to print out the following pattern of asterisks
without using more than three PRINT statements.
* * * * * * * * *
* * * * * * *
* * * % *
% * *
*
11. Write a graphics program that draws a grid on the screen (a set of
evenly spaced horizontal and vertical lines).
12. N! is read “N factorial” and means the product of all the integers
from 1 to N inclusive. For example,
3! = (1)(2)(3) = 6
5! = (1)(2)(3)(4)(5) = 120
and so on. Write a program calls for the input of N and then
computes and prints out N!
13. Write a BASIC program that calls for the input of N grades and
computes and prints out (1) the highest grade, (2) the lowest grade,
and (3) the average of the grades.
14. What, if anything, is wrong with the following program?
100 FOR X =1 TO 2
110 FOR Y=2 TO 6
120 PRINT X+Y
130 NEXT Y
140 FOR Z=1 TO 3
150 PRINT X+Z
156 Hands-on BASIC
160 next x
170 NEXT Z
180 END
15. What will be output if you run the following program?
100 FOR X=1 TO 4
110 FOR Y =1 TO 3
120 LET Z=X*Y
130 PRINT Z,
140 NEXT Y
150 PRINT
160 NEXT X
170 END
16. Suppose you decide to invest $1000 on the first of each year for ten
years at an annual interest rate of 6 percent. At the end of the tenth
year, the value of the investment will be $13,971.64. To see how
this could be computed, use the following formula:
$NEW = (SOLD + I)(l + R/100).
In this formula, R is the annual interest rate in percentage. I is
the annual investment, SOLD is the value of the investment at the
beginning of each year, and $NEW is the value of the investment at
the end of the year. Thus, $NEW becomes SOLD for the next year.
Write a BASIC program that will produce the following output.
WHAT IS THE ANNUAL I NUESTMENT? (You type in)
THE ANNUAL INTEREST RATE < X >? (You type in)
HOW MANY YEARS? (You type in)
AT THE END OF THE LAST YEAR THE UALUE OF
THE INUESTMENT WILL BE (Computer types answer)
17. The DATA statements below contain the time worked by a number
of employees during a one—week period.
190 DATA 5
200 DATA 2, 4
201 DATA 5.. 3
202 DATA 1.. 3
203 DATA 4.. 5
204 DATA 3.. 4
.. 1 0 .. 8 .. 7 > 1 0
7 , 8 .■ 8 . 6 . 10
8 .. 1 0 .. 6 , 8 .. 8
10 , 6 .. 10 .■ 6
6 , 6 , 8 , 10 , 7
Looping and Functions 157
The number in line 190 gives the number of employees to follow.
Each of the DATA lines after line 190 contains a weekly record
for one employee. The data are the employee number, the hourly
rate, and the hours worked Monday through Friday. The employee
receives time and a half for everything over 40 hours per week.
Write a BASIC program using these DATA statements to compute
and print out the employee number and the gross pay for the week
for each of the employees.
18. Assume that the following DATA statements give the performance
of the students in an English class on three examinations:
30
DATA
6
0 0
DATA
"7
30
85,
yv
01
DATA
1,
75,
80,
71
02
DATA
b .«
1 0 0
, w .c!
81
03
DATA
5,
40,
55,
43
04
DATA
i .i
6 0 ,
71 ,
68
05
DATA
4,
70
47,
42
The number in line 190 is the number of students in the class. Each
of the DATA statements that follow gives the performance for a
single student. The information is the student ID number, grade
1, grade 2, and grade 3. Thus, as shown in line 202, student 6 got
examination grades of 100, 82, and 81. Write a program using these
DATA statements to compute and print out each student's ID number
and his or her course grade. Assume that the first two examination
grades are weighted 25 percent each toward the overall grade and
the last grade is weighted 50 percent.
7-6 PRACTICE TEST
1. What will be printed if you run the following program?
100 FOR Y=28 TO 1 STEP -2
110 PRINT V,
120 NEXT Y
130 END
158 Hands-on BASIC
2. What will be printed out if you run the following program?
100 FOR A=1 TO 4
110 FOR B=1 TO 3
120 PRINT A*B,
130 NEXT B
140 NEXT A
150 END
3. Fill in the blanks.
a. SQR(36) = _
b. INT(7.13) = _
c. ABS(—22.8) = _
d. SGN(—1.3) = _
4. What, if anything, is wrong with the following program?
100 FOR 1=1 TO 5
110 FOR J=2 TO 5
120 PRINT I, J
130 NEXT I
140 NEXT J
150 END
5. Miles can be converted to kilometers by multiplying the number of
miles by 1.609. Write a program to produce the following output:
MILES KILOMETERS
10
15
20
etc.
1 00
16.09
24.135
32 . 18
16 0 . 9
Looping and Functions 159
6. Numerical information is loaded into DATA statements as follows:
100 DATA 10
110 DATA 25,21,24,21,26,27,25,24,23,24
The number in line 100 gives the number of numbers to be processed
in the rest of the DATA statements. Write a program using these
statements to compute the average of the numbers excluding the one
in line 100.
7. Study the following program.
100 GRAPHICS 8
110 COLOR 1
120 FOR UERT=0 TO 120 STEP 40
130 FOR HRZ = 0 TO 240 STEP 40
140 PLOT HRZ,UERT : DRAWTO HRZ,UERT+15
150 DRAWTO HRZ+10,UERT+15
160 DRAWTO HRZ,UERT
170 NEXT HRZ
180 NEXT UERT
190 END
a. What shape will be drawn when you run the program?
b. How many copies of the shape will be drawn?
c. Are the shapes drawn across first or down first?
CHAPTER 8
WORKING WITH
COLLECTIONS
OF NUMBERS
8-1 OBJECTIVES
In this chapter you will apply some of the ideas you learned earlier
to collections of numbers. You will be introduced to new concepts
that will expand the capability of BASIC.
Learning to Use Single— and Double— Subscripted Variables
You will learn what subscripted variables are and how to use them
to create more useful programs.
Saving Space for Arrays
When you want to store a collection of numbers in the computer,
you must indicate how much space the numbers will occupy in the
memory. You will learn how to use the DIM statement to save space
in the computer's memory.
Using FOR NEXT Loops to Handle Subscripted Variables
You will learn to apply FOR NEXT loops to the repetitive process
of naming numbers in a collection.
Working with Program Examples
You will study BASIC programs that take advantage of subscripted
variables.
162 Hands-on BASIC
8-2 DISCOVERY EXERCISES
Subscripts
When working with groups of numbers you must be able to distin¬
guish members of the group from one another. This is the reason
for subscripts. Before learning about subscripts, however, add two
important words to your computer vocabulary. You could use the
word collection to describe a group of numbers, but two other words
are more commonly used: matrix and array . For our purposes they
both mean the same thing: a “collection of numbers." Remember,
then, the terms matrix and array mean a collection of numbers.
■ MATRIX and ARRAY mean collections of numbers.
Let's look at the array below.
Yi =9
Y 2 = 10
Y s = 7
Y 4 = 14
r 5 = 12
n = is
The name of the array is Y. Its size is six, since there are six
elements (or numbers) in it. The numbers 9, 10, 7, 14, 12, and
15 are the elements in the array. The numbers printed to the right
and slightly below the Ys are called subscripts. In BASIC, subscripts
are printed in parentheses, e.g., Y(3) rather than Y 3 . Each subscript
merely points to one element in the array. Thus, Y(4) means the
fourth number in the array, which in this case is 14. We" read Y(4)
as “Y sub four." The third number in the array would be called "Y
sub three," and so on.* This array is one-dimensional, since it takes
only a single number (or subscript) to locate a given element in the
array.
Working With Collections of Numbers 163
Now let's look at a more complicated example.
Zi,i
= 4
Zi ( 2 — 9
GO
II
Z2,l
= 3
Z2,2 — 8
^2,3 = 7
In this example, there are six elements in the array Z. However,
this is a two-dimensional array, since we must specify which row
and column we want. The first subscript gives the row number;
the second specifies the column. Z 2 ,i is read as "Z sub two one"
and means the element of Z at the second row and first column.
Likewise, the element at row 1, column 3 would be identified as Z 1;3
and would be read "Z sub one three."
In summary, you will work with two kinds of matrices or
arrays. Elements in a one-dimensional array are located with a
single number. Elements in a two-dimensional array are located
with two numbers, designating a row and a column. A location
in a one-dimensional array is designated by a single-subscripted
variable. Likewise, the double-subscripted variable is used in the
two-dimensional array. You are now ready for the computer work.
Turn on the computer, bring up ATARI BASIC, and enter the fol¬
lowing program:
100 LET X<
110 LET X<
120 LET X<
130 LET
140 LET X'
150 PRINT
160 END
What do you think will be printed out if you run the program?
1 >=21
2 >=13
3 >=16
4 > = S
5 >=11
X< 1 >
Run the program and record what happens.
164 Hands-on BASIC
Error 9 is a dimension error that will be considered in greater detail
later. Type in
90 DIM X< 5 >
Run the program again and record what happens.
2. Now modify the program to print out the fourth value of X. Run
the program. Did it work?
L
3. Now type
150 PRINT X<3 )+X<4 }
Display the program and study it briefly. What do you think will
happen if you run the program?
Run the program and see if you were right. Record the output.
i_
4. Type
150 FOR 1=1 TO 5
152 PRINT X<I>
154 NEXT I
Display the program. What do you think will be printed out?
See if you were right. Record what happens when you run the
program.
Working With Collections of Numbers 165
5. Modify this program to print out only the first three values of the
array X. Record what happens.
6. Again modify the program, but this time so that the first value of
the array, then every other one, will be printed out. Record what
happens.
7. Clear the program in memory. Enter the following program:
90
DIM YC 2
.* 3 )
1 0 0
LET YC
i , i
• l — 2
110
LET YC
1 , 2
_ nr
• — J
120
LET YC
1 , 3
:■= 1
130
LET YC
2, 1
= ill
140
LET YC
O *”
L—
:* = 4
150
LET YC
t "7
\i — ~? t
160
1 70
PRINT
END
YC 1 ,
.7 )
Display the program and make sure you have entered it correctly.
What do you think this program does?
Run the program and record the output.
8. Type
i 60 PR I NT Y < 2 j 2 )+Y< 1.« 3 )+Y< 1,1)
Display the program. What will this program do?
L
Run the program and see if you were right.
166
Hands-on BASIC
9. Type
160 LET S=0
162 FOR J=1 TO 3
164 LET S =o + Y 1 * J
166 NEXT J
168 PRINT S
Display the program and study it carefully. What will happen if you
run this program?
Run the program and record the output.
L
Explain in your own words what is taking place.
L
10. Type
162 FOR 1=1 TO 2
164 LET S=S+YCI,2>
166 NEXT I
Display the program. What is the program doing now?
Run the program and record the output.
L
Again try to explain in your own words what is happening.
Working With Collections of Numbers 167
11. Now type
164
FOR J =
166
LET S =
168
NEXT J
170
NEXT I
172
PRINT
180
END
Display the program and think a minute about it. In particular,
compare what you see now to what happened in steps 9 and 10.
What does this program do?
Run the program and record the output.
12, Clear the program in memory. Type the following program:
1 0 0
DIM X
< 4
y .. v < 4 >
110
FOR I
= 1
TO 4
120
READ
A _■
B
130
LET X
< I
) = A
140
LET V
< I
> = B
150
NEXT
I
160
PRINT
y
<1>+Y<4
170
DATA
2.«
1
171
DATA
-l
“7
172
DATA
cr
j t
f.
173
DATA
2 .*
4
180
END
Display the program and check to see that you have entered it
correctly. Study the program carefully. If you run the program,
what will be typed out?
168 Hands-on BASIC
Run the program and see whether you were right. Record the output.
L
13. Clear the program in memory. Type the following program:
1 0 0
DIM A
if
4
~7
)
110
FOR I
=
1
T
0
4
120
FOR J
=
1
T
n
“7
130
READ
T
140
LET A
(
I
.. J
*:« z
=T
150
NEXT
J
160
NEXT
I
170
FOR I
=
1
T
0
4
180
FOR J
=
1
T
0
“7
190
PRINT
A
< I
J >
2 0 0
NEXT
J
210
PRINT
220
PRINT
230
NEXT
I
240
DATA
1
..
“7
1
250
DATA
4
..
2.»
5
260
DATA
1
,
4 >
2
270
DATA
7 ,
!
2 *
5
2 8 0
END
Make sure that you have entered the program correctly, then take a
few minutes to study it. Notice the two spaces between the quotes
in line 190. Can you see what will be printed out if you run the
program?
Run the program and record the output.
Compare what was printed out to the numbers in the DATA state¬
ments in the program.
Working With Collections of Numbers 169
14. Clear the program in memory and then enter the following program:
1 0 0
DIM AC2,2)
110
FOR 1=1 TO
120
INPUT X,V
130
LET AC 1,1> =
C. 1
«*'*k
140
LET AC 1,2 :■ =
Y
150
NEXT I
160
PRINT
170
PRINT
180
FOR 1=1 TO
130
FOR J=1 TO
“i
200
PRINT AC I,J
! )
210
NEXT J
220
PRINT
230
PRINT
240
NEXT I
250
END
Run the program and when the INPUT prompt appears, type
2,5
3,8
What happens?
Compare the output to the numbers you typed in.
15. Clear the program in memory. Then enter the following program:
100 DIM X< 3.. 3)
110 FOR 1=1 TO 3
120 FOR J=1 TO 3
130 READ A
140 LET XCI,J >=A
150 NEXT J
160 NEXT I
170 Hands-on BASIC
178
PRINT
188
PRINT
190
FOR 1=1
TO 3
2 8 0
FOR J=1
TO 3
210
PRINT X
( I, J }
220
NEXT J
230
PRINT
240
NEXT I
250
DATA 2..
1,3
260
DATA 4 .■
7,5
278
DATA 1,
2.« 6
2 8 8
END
Run the program. What happens?
L
Compare the output to the numbers in the DATA statements.
16. This concludes the computer work for this chapter. Turn off the
computer.
8-3 DISCUSSION
Most students are confused by arrays. Pay particular attention to
the discussion material to clear up any questions that might have
arisen in the computer work.
Learning to Use Single—and Double—Subscripted Variables
The need for subscripted numbers becomes obvious when you handle
large collections of numbers. If, for example, you were writing
a program that involved only four numbers, you would have no
difficulty naming them. You might call the numbers X, Y, U, and V.
But suppose you needed to work with 100 numbers. For this reason,
it is often very useful to have subscripted numbers. Fortunately,
BASIC makes provisions for subscripts.
Working With Collections of Numbers
171
Consider the following set of numbers:
i Yi
1 14
2 8
3 9
4 11
5 16
6 20
7 5
8 3
We can refer to the entire set of numbers by the single name Y. Thus,
Y is a collection of numbers, a matrix, or an array— all of which
mean roughly the same thing for our purposes. To locate a number
in an array, we must have the array name (in this case Y) and the
number's position in the array. The i column gives the number's
position. Thus Y(3) (pronounced “Y sub three") locates the third
number in the array Y. In this case, Y(3) has the value 9. Likewise,
Y(7), is 5, Y(l) is 14, and so on. Y(i) (pronounced “Y sub i"), is a
general way to denote any element of the array, depending on the
value of i. In the example above. If i were 8, then Y(i) would be
3. This collection of numbers is one-dimensional, since only one
number (subscript) is needed to locate any element in the array.
Next let's look at a two-dimensional array.
Y itj 12 3 4
1
3
-1 10
8
2
2
4 5
6
3
1
-2 9
3
Now you need two numbers to locate an element in the array. Given
a row number and a column number, you can find any element of
the array. For example, Y(l,3) means the element of Y located at
row 1, column 3. In the example above, the element has the value
10. A general way to denote an element in the two-dimensional
array is Y(i,j). The first subscript (i) is the row number, and the
second subscript (j) is the column number.
1 72 Hands-on BASIC
To make sure you understand how the double subscripts are
used, refer to the two-dimensional array in the table above and verify
that the following statements are correct:
r 3 ,2 — —2
Y 1A = 8
Y 3 ,3 = 9
Y 2t i = 2
■ Double subscripts define row and column numbers.
An interesting question comes up. Does X(M — N + 3,S*T)
mean anything? The answer is yes provided that the computer can
convert M— NT3 and S*T into numbers. Even Y(Y(1,1),Y(2,3)) is all
right as long as the computer can locate the numbers in Y(l,l) and
Y(2,3). However, suppose you want to locate X(A + B) where A =
2.6 and B = 1.1. Thus, A + B = 3.7. But it doesn't make any sense
to try to look up the 3.7th number in the array X. In this case, the
computer will take only the integer in 3.7, and compute X(A + B) as
X(3), the third element in the array X.
Saving Space for Arrays
The computer must know how big an array is for two reasons.
First, it must allow sufficient space in memory to hold the array.
Next, the computer must know the size of the array in order to carry
out arithmetic operations properly.
■ Save space with a DIM statement.
An example of a DIM (for “dimension") statement is
1 0 0 DIM B£ 5 .« 2 0 ) .. Y ( S ) .* Z< 34 >.. X ( 3 .* 6 j
Four arrays are “dimensioned" in line 100. B is a two-dimensional
array with five rows and twenty columns. Y is one-dimensional,
with eight elements. Likewise, Z is one-dimensional, with thirty-four
Working With Collections of Numbers 173
elements. Finally, X is a two-dimensional array with three rows and
six columns. It's a good practice to make the DIM statement the first
one of the program because you can see the sizes of the arrays that
will be used by glancing at the beginning of the program. However,
the DIM statement must appear before any other statement that
refers to arrays.
Using FOR NEXT Loops to Handle Subscripted Variables
Subscripts involve collections of numbers. Because operations with
collections of numbers almost always involve repetition, it is reason¬
able to employ FOR NEXT statements to handle arrays. You will
use FOR NEXT loops to define the subscripts used in the arrays. For
example, the following program segment sets up a six by four array,
then load 5s into all the elements.
1 0 0
DIM AC b,
, 4 )
110
FOR R=1
TO
120
FOR C=1
TO
130
LET ACR.
. C >
140
NEXT C
150
NEXT R
If you study this program segment, the details of the process
become clear. When the computer reaches line 130 in the program
for the first time, R = 1 and C = 1. Then R is held constant while C
goes to 2, 3, and 4. At each step in this process, the corresponding
element of the array is set equal to 5. Then R is set equal to 2, and
C takes on the values 1, 2, 3, and 4. The process goes on until all
the elements of the array have been set equal to 5.
Either one- or two-dimensional arrays can be handled in this
fashion using subscripts. In many applications it is preferable to use
FOR NEXT loops to carry out the desired operations on arrays.
An important fact about subscripted variables is that they
cannot be used directly in INPUT or READ statements. Therefore,
it is necessary to use non subscripted variables first and then use the
LET assignment statement. For example, the program segment
100 DIM AC3)
110 FOR 1=1 TO 3
120 INPUT X
130 LET A<I )=X
140 NEXT I
174 Hands-on BASIC
shows how the variable X is used to contain the value that is typed
in at the keyboard. Then the assignment statement
180 LET R<I>=X
transfers the value to the subscripted variable A(I), This is done for
all three values. The LET statement allows you to use the INPUT
and READ statements indirectly with subscripted variables.
8-4 PROGRAM EXAMPLES
Example 1 - Examination Grades
Suppose the distribution of examination grades in a class of fifteen
students is as follows:
Student Number
_ | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Grade 67 82 94 75 48 64 89 91 74 71 65 83 72 69 72
The problem is to write a BASIC program that allows you to
type in the grades. The format should be:
HON MANY STUDENTS? (You type in)
STUDENT GRADE
1 (You type in grade, etc.)
(etc.)
The program should instruct the computer to find the class average,
the highest grade, and the lowest grade, then print this information
out as follows:
CLASS AUER AGE IS (Computer prints out average)
HIGHEST GRADE IS (Computer prints out highest grade)
LOWEST GRADE IS (Computer prints out lowest grade)
Let's approach the problem by steps. First, since you are going
to store the student grades in subscripted form, you must include a
DIM statement to save space for the array.
Working With Collections of Numbers 175
100 DIM L(50 >
You are using the variable G to store grades and can insert up to
fifty grades. Next you have a message, an input, and a space.
110 PRINT "HOW MANY STUDENTS ";
120 INPUT N
130 PRINT
Now you are ready to input the grades. First you must
generate the heading for the table.
140 PRINT "STUDENT", "GRADE"
150 PRINT
A loop using FOR NEXT statements is ideal to control the
input of grades.
168 FOR 1=1 TO N
170 PRINT I,
180 INPUT A
190 LET G<I>=A
200 NEXT I
The student number is printed out in line 170. In line 190, the
student number (I) is used as a subscript for the grade. This line
generates grades in the computer in the form G(l), G(2),...,G(N).
The next task is to find the average of the grades. This can be done
by summing up all the grades and dividing by the number of grades.
210 LET S — 0
220 FOR 1=1 TO N
230 LET S=S+G<I )
240 NEXT I
250 PRINT
Now you can program the computer to find the average and print
out the results.
260 LET M = SN
270 PRINT "CLASS AUERhGE IS " i M
176 Hands-on BASIC
The final part of the program is to locate and print out the
highest and lowest grades in the class. H and L will stand for the
highest and lowest grades, respectively. Initially, set both H and L
equal to G(l), the first grade in the list. You know that the same
grade can’t be the highest and lowest at the same time. Thus, you
will program the computer to go through the rest of the grades,
compare H and L with each grade, and make adjustments to H and
L as required.
288 LET H=G
290 LET L=G
3 8 0 FOR 1=2
310 IF L<G<
320 LET L=G
330 IF H>G<
340 LET H=G
350 NEXT I
< 1 >
< 1 >
TO N
I >
THEN 330
< I
i
I >
THEN 350
< I
The required printout can be obtained with two lines.
360 PRINT "HIGHEST GRADE IS " .= H
370 PRINT "LOWEST GRADE IS ";L
Finally the END statement completes the program.
380 END
The complete program follows:
100 DIM G<50>
110 PRINT "HOW MANY STUDENTS "
120 INPUT N
130 PRINT
140 PRINT "STUDENT", "GRADE"
150 PRINT
160 FOR 1=1 TO N
170 PRINT I,
180 INPUT A
190 LET G<I 3=A
200 NEXT I
210 LET S=0
220 FOR 1=1 TO N
Working With Collections of Numbers 177
230 LET S=S+U<I>
240 NEXT I
250 PRINT
260 LET M=S/N
270 PRINT "CLASS AUER AGE IS ".; M
280 LET H=GC1>
290 LET L= G(1>
300 FOR 1=2 TO N
310 IF L<G<I> THEN 330
320 LET L=G<I>
338 IF H>G<I> THEN 350
340 LET H=G< I ;■
350 NEXT I
360 PRINT "HIGHEST GRADE IS ";H
370 PRINT "LOWEST GRADE IS "L
380 END
Turn on the computer, bring up ATARI BASIC, and run this
program using the data at the beginning of the example. If you have
any difficulty with the highest and lowest search in lines 280 through
350, trace the program in detail.
Example 2 - Course Grades
You can easily extend the ideas in example 1 to a two-dimensional
array. Suppose the class has ten students, and the course grade is
based upon five examinations. Typical results for such a class might
be
Student Number
1 1
2
3
4
5
6
7
8
9
10
1
92
71
81
52
75
97
100
63
41
75
2
85
73
79
49
71
91
93
58
52
71
Exam 3
89
74
80
61
79
88
97
55
51
73
4
96
68
84
58
80
93
95
61
47
70
5
82
72
82
63
73
92
93
68
56
74
You can use an array with a FOR NEXT statement to READ
the data from DATA statements. The computer is to find and print
out the following information:
178 Hands-on BASIC
STUDENT COURSE RUE
(Computer prints average, etc.)
CLASS RUE
(Computer prints average, etc.)
The program should start with a DIM statement although the
DATA statements can go anywhere in the program.
100 DIM G< 5 ,10 >
This statement reserves memory space for an array with five rows
and ten columns. The row number (R) will be the examination
number, and the column number (C) will correspond to the student
number.
1
etc.
TEST
1
etc.
110
DATA
9 2, 71 .
81,52,75,97,100
,63,41
, r
120
DATA
85,73.
79,49,71,91,93,
58,52,
71
130
DATA
89,74.
80,61,79,88,97,
55,51,
73
140
DATA
96,68■
84 * 58.80.93,95.
61,47,
70
150
DATA
IJ Z { ^ J
O •”» fT "7 “7 "7 Q O Q “7
68 ■ 56 .
74
All the numbers can be read into the program with the fol¬
lowing FOR NEXT statement.
160 FOR R=1 TO 5
170 FOR C=1 TO 10
180 READ A
190 LET G < R , C ) = A
200 NEXT C
210 NEXT R
You have just programmed the numbers to be read into the matrix
G by rows. Thus, the data in line 110 become row 1 of the matrix
G, and so forth. Before doing anything else, print out the required
headings.
Working With Collections of Numbers 179
220 PRINT "STUDENT'S "COURSE HUE"
230 PRINT
Now you can compute the course average for each student.
240 FOR C=1 TO 10
Line 230 opens a loop that will look at each column in the matrix.
For each value of C, the computer must find the column average and
print it out.
250 LET S=0
260 FOR R=1 TO 5
270 LET S=S + G (. R.. C >
280 NEXT R
290 PRINT C,S.-"5
Then close the C loop.
300 NEXT C
Now the process is repeated except that the averages are com¬
puted on rows rather than columns.
310 PRINT
320 PRINT "TEST, "CLASS HUE"
330 PRINT
340 FOR R=1 TO 5
350 LET S=0
360 F 0 R C=1 T 0 10
370 LET S=S+G< R.. C >
380 NEXT C
390 PRINT R, S10
400 NEXT R
Finally the END statement.
410 END
180 Hands-on BASIC
The complete program follows:
1 00
DIM G
< 5, 10 >
110
DAT A
32, 71,
81,52.
75,97,100,b
3,41
,75
120
DATA
85,73,
79,43.
71,91,93,58
, 52,
71
130
DATA
89,74,
80,61.
79,88,97,55
,51,
r J
140
DATA
9h » hr! .
84,58.
Hfi , 97, , 95 . f. 1
, 47,
70
150
DATA
“i ■“ *■? - - «
O il , t i— ,
8 2, b 3,
73,32,93,b y
, 5b,
74
160
FOR R
= 1 TO
c*
-_i
170
FOR C
= 1 TO
10
180
READ
A
—
190
LET G
( R .« L i —-
A
200 NEXT C
210 NEXT R
220 PRINT "STUDENT", "COURSE HUE"
230 PRINT
240 FOR C=1 TO 10
250 LET S=0
260 F 0R R=1 T 0 5
270 LET S=S+G(R,C >
280 NEXT R
290 PRINT C,S/5
300 NEXT C
310 PRINT
320 PRINT "TEST", "CLASS HUE"
330 PRINT
340 FOR R=1 TO 5
350 LET S=0
360 FOR C=1 TO 10
370 LET S=S+G<R,C>
380 NEXT C
390 PRINT R, S--10
400 NEXT R
410 END
This program illustrates valuable programming techniques in¬
volving arrays. It is worth studying and executing on your computer.
Example 3 - Array Operations
The final example is a series of short programs that will be given
without explanation. Study each program until you are sure you
understand what is taking place.
Working With Collections of Numbers 181
a. Write a program using FOR NEXT loops to load a three by four
array with Is.
100 DIM 3.. 4>
110 FOR R=i TO 3
120 FOR C=1 TO 4
130 LET K(RjC)=1
140 NEXT C
150 NEXT R
160 END
b. Write a program to generate and load the numbers
2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048
into a one-dimensional array.
100 DIM ZCUJ
110 LET Z<1>=2
120 FOR 1=2 TO 11
130 LET Z<I>=2*Z<1-1 )
140 NEXT I
150 END
c. Write a program to read in the array
2 3 5
1 4 2
from DATA statements and then print out the array.
10 0 DIM A ( 2 .• 3 >
110 FOR R=1 TO 2
120 FOR C=1 TO 3
130 READ X
140 LET h<R,C:j = X
150 NEXT C
160 NEXT R
170 FOR R=1 TO 2
180 FOR C=1 TO 3
190 PRINT A<R,C>,
200 NEXT C
182 Hands-on BASIC
10
PRINT
20
PRINT
30
NEXT
40
DATA
50
DATA
60
END
8-5 PROBLEMS
1. Write a program using the DATA statements
209 DATA 12
210 DATA 2, 1,4,3,2,4,5,6,3,5,4, 1
The program will read the size of an array from the first DATA
statement, read the elements of the array from the second DATA
statement, load them into an array X, and print out the array.
2. Write a program to fill a four-by-three array with 2s.
3. Write a program to call for the input of a square N by N matrix where
N is a whole number no larger than 10. Program the computer to
find and print out the sum of the entries on the main diagonal of
the array.
4. Write a BASIC program using the READ command to read twenty-
five numbers from the DATA statements into a one-dimensional
array named A. Program the computer to search the array and print
out the number of elements in the array that are greater than fifty.
Fill in the required DATA statements with any numbers you choose.
5. Write a program to call for the input of an M by N matrix. Assume
that both M and N are no larger than 15. Then have the computer
find and print out the sum of all the elements in the matrix.
6. The program below is supposed to compute and print out the sum
of the elements in a one-dimensional array that are positive but not
greater than 10. As it stands the program is incorrect. What's
wrong?
100 DIM AC 6 >
110 FOR 1=1 TO 6
120 INPUT T
130 LET AC I>=T
Working With Collections of Numbers 183
140 NEXT I
150 LET S=0
160 FOR 1=6 TO 1 STEF -1
170 IF ACI>>10 THEN 200
130 IF ACI )<0 THEN 200
190 LET S=S+ACI>
200 NEXT I
210 PRINT S
220 END
7. What will be output if you run the following program?
1 0 0
DIM Y
< 6 )
110
FOR I
= 1 TO
6
120
READ
H
130
LET Y
< I ) = R
140
NEXT
i
150
DATA
2,1,3,
1 , 2
160
LET S
1=0
170
LET S
2 = 0
180
FOR I
= 1 TO
b
1 9 Li
LET S
1 = S 1 + Y
C I >
2 0 0
LET S
2=S2+Y
C I )
210
NEXT
I
220
LET X
=S2-S1
2 3 0
PRINT
",
240
END
8. What will be output if you run the following program?
1 0 0
DIM AC 10
110
FOR 1=1
T 0 1 0
120
READ X
1 30
LET AC I>
=x
140
NEXT I
150
LET S = AC
1 >
1 60
FOR 1=1
TO 9
1 70
LET AC I>
= AC I + 1 )
180
NEXT I
190
LET AC 10
> = s
2 0 0
FOR 1=1
T 0 1 0
210
PRINT AC
I >
220
NEXT I
230
DATA 10,
9,8,7,6,5,4,3,2, 1
240
END
184 Hands-on BASIC
9. What will be printed out if you run the following program?
100 DIM X( 4 .• 4)
110 FOR 1=1 TO 4
120 FOR J=1 TO 4
130 READ A
140 LET K<I,J>=A
150 NEXT J
160 NEXT I
170 DATA 1,2,3,4,2,3,4,5
18 0 DATA 3 .. 4 .. 5.. b .. 4 .. 5 .. 6 .• 7
190 LET S — 0
200 FOR 1=1 TO 4
210 LET S=S+X< I,5-1>
220 NEXT I
230 PRINT S
240 END
10. What will be printed out if you run the following program?
100 DIM Y<4,4>
110 FOR R=1 TO 4
120 FOR C=1 TO 4
130 LET Y<. R, C >=0
140 NEXT C
150 NEXT R
160 FOR R=1 TO 4
170 FOR 0=1 TO 4
180 LET Y< R,C > = R*C
190 NEXT C
200 NEXT R
210 FOR R=1 TO 4
220 FOR C=1 TO 4
230 PRINT Y(R,C)i" "i
240 NEXT C
250 PRINT
260 NEXT R
270 END
Working With Collections of Numbers 185
11. Write a BASIC program to call for the input of N (assumed to be
a whole number between 1 and 100), then input a one-dimensional
array with N elements. The program should sort the array into
descending order, and finally print out the sorted array.
12. Let's assume that the first number in the DATA statements gives the
number of pieces of data to follow. Assume that the pieces of data
are all whole numbers between 1 and 10 inclusive. Write a program
that will compute the number of Is, 2s, etc., in the data and then
print the information. (Hint: Use the data as they are read in as
a subscript to increment an element of an array used to count the
numbers.)
13. What will be printed out if you run the following program?
1 0 0
DIM ZCb,
6 j
110
FOR R=1
TO
6
120
FOR C=1
TO
b
130
LET Z(.R,
C >
= 0
140
NEXT C
150
NEXT R
160
FOR R=1
TO
c
•_«
170
FOR C = R
TO
b
180
LET Z(R,
C )
= 1
190
NEXT C
2 0 0
NEXT R
210
FOR R=1
TO
6
2 2 0
FOR C=1
TO
b
230
PRINT Z<
R,
c >
240
NEXT C
250
PRINT
2 6 0
PRINT
270
NEXT R
2 8 0
END
14. If you run the program below, what will the computer print out?
100 DIM Ac5,5>
110 FOR R=1 TO 5
120 FOR C=1 TO 5
130 READ X
140 LET AC R.« C }=X
150 NEXT C
186 Hands-on BASIC
160
NEXT R
170
DATA 2..
i. •
i—. .* iL .• lL
■ j O “•
•' k u .' L
180
DATA £.■
O *-■
iL. L_ .»
d .
d f d j d
d j d .■ d
190
DATA 2..
-J “I
£l .
o
200
FOR C=5
TO
1
STEP
-i
210
FOR R=1
TO
c
220
LET A<R
c >=
“7
238
NEXT R
240
NEXT C
250
FOR R=1
TO
c
•J
260
FOR C=1
TO
nr
270
PRINT A
<: r , c
: > j
. li II .
2 8 0
NEXT C
290
PRINT
3 0 0
NEXT R
310
END
15. Write a program to read the following array from DATA statements,
then print out the array.
2 10 5 1
3 2 13 1
16. Write a program to read the following array from DATA statements,
then print out the array.
- 5 3"
2 0
-1 1
4 2
- 2 6 -
17. Write a BASIC program that will call for the input of an M by N
array. The program should then compute and print out the sum of
the elements in each row and the product of the elements in each
column.
18. Write a BASIC program that will read two arrays from DATA state¬
ments. Both the arrays are two by three. Then have the program
compute a third two-by-three array such that each element is the
sum of the corresponding elements in the first two arrays. Print out
the third array.
Working With Collections of Numbers 187
19. The data below represent sales totals made by salespeople over a
one-week period.
—
Mon
Tue
Wed
Thu
Fri
Sat
1
48
40
73
120
100
90
Salesperson ^
75
130
90
40
110
85
50
72
140
125
106
92
4
108
75
92
152
91
87
Write a program that will compute and print out
a. The daily sales totals
b. The weekly sales totals for each salesperson
c. The total weekly sales
20. Write a program to call for the input of a four-by-four matrix.
The program should compute a new matrix from the first with the
rows and columns interchanged. That is, row 1 of the input matrix
becomes column 1 of the new matrix. Row 2 of the input matrix
becomes column 2 of the new matrix, and so on. Finally, have the
program print out the new matrix.
21. Consider the two arrays below:
P X
1 28
nr
-J l!
3 14
b 3
4 17
Each element of P “points” to an element of X. P(l) = 1 and
X(l) = 28. P(2) — 5 and X(5) = 17. If you keep this process up,
the values of X are listed in descending order. Write a program to
set up two arrays X and P to some convenient length. Then call
for the input of arbitrary values of X from the keyboard. Construct
the array P so that its elements point to X in descending order as
illustrated above. Then print out the two arrays as shown.
188 Hands-on BASIC
8-6 PRACTICE TEST
1. What is the purpose of the DIM statement?
2. We have an array named X. What variable name does BASIC use to
locate the element in row 3, column 4?
3. Use an array in a progam to input a list of numbers, then find and
print out the sum of the positive numbers in the list. The printout
should look as follows:
HOW MANY NUMBERS? (You type in the number)
WHAT ARE THE NUMBERS? (You type them in)
THE SUM OF POSITIVE ELEMENTS IS (Computer
types out answer)
4. Write a program using FOR NEXT statements to load a four by six
array with 4s.
5. What will be printed out if you run the following program?
1 0 0
DIM AC
cr
•_J j
■ 5 >
110
FOR 1 =
1
TO
nr
120
FOR -J =
1
TO
cr
139
LET AC
R,
■ c > =
0
140
NEXT J
150
NEXT I
160
FOR 1 =
1
TO
c
.J
170
LET AC
I ,
. I >=
: i
180
NEXT I
190
FOR 1 =
1
TO
c
200
FOR J =
1
TO
5
210
PRINT
AC
: i, j
j
220
NEXT J
230
PRINT
240
PRINT
Working With Collections of Numbers 189
250 NEXT I
260 END
L
6. The following array is named A:
[l 3 5
[6 2 4
a. Write a DIM statement for A.
L
b. What is the value of A(2,3)?
c. If X = 1 and Y = 2, what is A(X,Y)?
d. What is A(A(1,1),A(2,2))?
CHAPTER 9
STRING VARIABLES
9-1 OBJECTIVES
Some of the most important applications of computers deal with
characters rather than numbers. In this chapter you will learn to
handle strings of characters as “string variables .”
Handling String Input and Output
Before meaningful operations can be carried out on strings you must
learn how to input and interpret output of string variables.
Using String Functions
You have already studied BASIC functions that operated on num¬
bers. Now you will turn to functions that work on strings of charac¬
ters.
Working with Program Examples
Your final goal is to write programs that work with string variables.
192 Hands-on BASIC
9-2 DISCOVERY EXERCISES
1. Turn on the computer, bring up ATARI BASIC, and enter the fol¬
lowing program:
90 DIM A$< 50 >
100 INPUT m
110 PRINT
120 PRINT m
130 PRINT h$
140 END
The A$ in the program identifies the variable as a string variable.
Run the program and type in your full name at the input prompt
(the question mark). What happened?
L
2. Now edit line 90 to read
90 DIM A$( 4 >
Run the program and again type in your full name at the input
prompt. What happened this time?
Clearly, the dimension of the variable must be large enough to cover
anticipated inputs.
3. Now modify the program as follows:
90 D IM A$< 50 ;■. B$< 50 ;■
100 INPUT m
110 INPUT B$
120 PRINT
130 PRINT B$
140 PRINT h$
150 END
String Variables 193
If you run the program and type the words INTELLIGENT and
CONVERSATION at the input prompts, what do you think will
be printed out?
Try it and record the output.
4. Let's try a different variation. Clear the program and enter the
following:
9 0 DIM X$< 50 >, Y$< 58 >
100 READ X,X$, Y , Y$
110 DATA 10,HERB,20,CHARLIE
120 PRINT X,Y
130 PRINT X$,Y$
140 END
This program contains several new ideas. What do you think will
happen if you run the program?
Run the program and record the output.
i_
5. Now that you have seen that strings can be included in DATA
statements, you should go a bit further. Change line 100 to read
100 READ X$,X,Y,Y$
What will happen if you try to run the program in this form?
See if you were right. Record below what happened when you tried
to run the program.
194 Hands-on BASIC
Error 8 is an attempt to input a string into a numeric variable. The
type of information in the DATA statements must match the type of
variable in READ statements.
6. Now on to a different topic. Clear the program and enter the
following:
90 DIM CSC 50 >
100 INPUT C$
110 LET N=LEN<C$>
120 PRINT N
130 END
The new feature in this program is the function LEN(CS). It works
on a string (in this case C$) rather than a number. Can you guess
what the function does?
Notice that the result of the function LEN operating on a string must
be a number since the result is assigned to a numeric variable N.
7. Run the program and at the input prompt type in ABCDE. What
was printed out?
Try it again, but this time type in AARDVARK. Record the output.
By now you should have a pretty good idea what the LEN function
does.
8. If you ru n the program and at the input prompt merely press the
RETURN] key, what do you think will be printed out by the computer?
Try it and see if you were correct. Now run the program and at
the input prompt type in R O B E R T. Note the spaces between the
characters. Record the output.
i_
String Variables 195
In the LEN function, do spaces count as characters?
9. Now you want to be able to specify a substring in a given string.
That is, given a string A$, how can you specify the Mth through
Nth characters of that string? The function that gives this substring
is A$(M,N).
10. Now clear the program in memory and enter the one below:
90 DIM A$<50>
100 INPUT A$
110 PRINT "M = M ;
120 INPUT M
130 PRINT "N = "i
140 INPUT N
150 PRINT A$<M,N>
160 G0TO 110
170 END
Run the program and at the input prompt for the string, type
MISSISSIPPI. Note that the length of the string is 11. Enter 4 for
M and 8 for N. Record the output.
i_
Now enter 7 for M and 9 for N. Again, record the output.
This time enter 1 for M and 4 for N and record the output.
196 Hands-on BASIC
11. Jump the computer out of the input loop, clear the program from
memory, and enter the one below:
90 DIM 50 >
lee input m
110 INPUT I
120 PRINT m< I , I >
130 PRINT
140 G0TO 110
150 END
Run the program and at the first input prompt type in
ABCDEFGHIJKLMNOPQRSTUVWXYZ. At the second input
prompt type in 20. What happened?
Run the program again and type in 10 at the input prompt for I.
What happened?
Experiment with various values of I between 1 and 26. Describe in
your own words what happens when the computer is directed to
print out A$(I,I).
12. Now type 30 at the input prompt for I. What happened?
i_
By now you should understand fairly clearly what happens when the
computer prints out A$(I,I). Of course, in this instance, the value of
I is greater than the length of the string. We will return to this topic
in the discussion section.
13. Experiment on your own with this program. Try various strings and
different values of M and N until you understand exactly how the
A$(M,N) function works.
String Variables 197
14. Now on to a different topic. Clear the program in memory and enter
the following:
90 D IM A$< 50 >, BSC 59 >
100 INPUT m
lie INPUT B$
120 IF A$<B$ THEN 150
130 PRINT B$
140 GOTO 100
150 PRINT m
1 b 0 G 0 T 0 10 0
170 END
Take a few moments to study the program. Clearly, the interesting
part is in line 120 where the strings A$ and B$ are involved in an
IF THEN statement. In particular, what do you suppose A$ < B$
means with regard to strings?
L
The way to find out if you are right or not is to run a few test cases.
For example, run the program and at the first input prompt, type
DUCK; at the second prompt, type CHICKEN. Record the output.
15. This time type HOUSE followed by TELEVISION. Record the out¬
put.
Keep experimenting with words or letters of your choice until you
understand exactly what the expression A$ < B$ means. Once you
understand this, it should be easy for you to see what A$ = B$,
A$ > = B$, and A$ <> B$ mean.
198 Hands-on BASIC
16. Jump the computer out of the input loop. Clear the program in
memory. Go on to the next string variable statement. Enter the
following program:
100 INPUT N
110 PRINT CHR$< N >
120 GOTO 100
130 END
Now run the program and at the input prompt, type in 65. What
happens?
The program will keep looping through as long as you desire. This
time try 66. What happens?
You may also wish to try 43, 49, and 50.
17. By now, you have probably realized that CHR$ converts a position
number to its corresponding character in the set of characters the
computer uses. Experiment with this program trying out various
numerical inputs in the range 33 to 122. You should see that you
can refer to a character either by the character itself or by its position
number in the set of characters.
18. To see a portion of the total available character set, jump the com¬
puter out of the input loop, clear the memory and type in the fol¬
lowing program.
100 FOR N=33 TO 122
110 PRINT CHR$< N >j 11
120 NEXT N
130 END
You can see the entire ATASCII character set by referring to
Appendix C of the ATARI BASIC Reference Manual.
String Variables 199
19. Now on to a different topic. Clear the program in memory and type
the following program:
90 DIM A$C 58 )
100 INPUT A$
110 LET X=ASC<AS >
120 PRINT X
13 0 G 0 T 0 1 0 0
140 END
Run the program and at the input prompt, type Z. What happens?
This new function, ASC(A$), is just the reverse of CHR$(N). It
converts a character to its equivalent position number in the charac¬
ter set used by the computer. Use various letters and numbers and
compare your results to those you obtained in step 16.
20. There is one more detail to be seen to. Your computer should still
be at the input prompt waiting for A$ to be typed in. This time type
in POTATO. Record the output.
L
Now try PEA and note the results. The only similarity between the
two words is that they both have the same first letter. We will return
to this concept later.
21. Jump the computer out of the loop, clear the memory, and type in
the following program.
90 D I M A$< 50 >.. B$< 50 >
100 PRINT
110 INPUT m
120 INPUT B$
130 LET A$< LEN< AS >+l >=B$
140 PRINT A$
150 END
Run the program. At the input prompts, type HONEY and BEE
respectively. Record the output.
200 Hands-on BASIC
Now edit lines 90 and 130 and add lines 125 and 135 as follows:
90 DIM ASC 50 > .■ BSC 50 >.. CSC 1 >
125 LET C$=" "
130 LET ASC LENC AS >+1 >=C$
135 LET ASC LENC AS >+l >=B$
Run the program and again type in HONEY and BEE at the input
prompts. How many words are displayed?
22. Now let’s carry this idea one step further. Either modify the program
in memory or clear the memory and type in the following program.
90 DIM ASC 50 >, BSC 50 >, CSC 1 >, DSC 50 >
100 PRINT
110 INPUT AS
120 INPUT BS
122 LET 0$=“HELLO MY"
125 LET C$=" "
130 LET DSC LENC D$ :■ + 1 >=C$
132 LET DSC LENC DS >+l } = A$
135 LET DSC LENC DS >+ 1 >=B$
140 PRINT DS
150 END
Display the program and check its accuracy. Run the program and
again input HONEY and BEE at the input prompts. Record the
output.
23. This concludes the computer work for this chapter. Turn off the
computer and go on to the next section.
String Variables 201
9-3 DISCUSSION
Handling String Input and Output
As you have already seen, a set of characters surrounded by quota¬
tion marks is called a string. (The quotation marks are not part of
the string.) The new idea in this chapter is that the string can be
treated as a variable — the string variable.
The string variable is identified by appending a dollar sign ($)
to a name. Thus, BARNS, BOXS, and BS are string variable names.
Input and output of string variables are handled the same way
as for numeric variables except in one case. You can mix numeric
and string variables in the same BASIC statements. For example:
100 PRINT h$,X,y,Z$
110 INPUT H,M$
120 READ
However, you cannot follow a string variable with another variable
in an INPUT statement.
You must be careful that the input in either INPUT or READ
statements matches the type of variable given. In line 110 above, the
computer would be looking for a number and a string of characters
Note that the string variable follows the numeric variable. It would
not work the other way around. In addition, you must be aware
that you can type in 123456789 and if the computer is looking for
a string it will identify this quantity as a string, not as a number.
The reason is that the string, as has been pointed out, consists
of characters, and symbols 0 through 9 are part of the standard
character set that will be discussed later. If, however, the computer
is looking for a number and you type in ABCDEFGHI, you will get
an error statement.
Using String Functions
The LEN function is used to determine the length of a string. If, for
example, AS = "HOW NOW BROWN COW" then LEN(A$) = 17.
Note that the spaces are counted as characters. You can also have
a "null" string. If A$ = ttn (there is nothing inside the quotation
marks), then LEN(A$) = 0.
LEN(AS) gives the number of characters in AS.
202 Hands-on BASIC
A substring is a piece or segment of a string. Consider the
following program:
90 DIM R$< 20 >
100 LET A$= M ROBERT E. LEE i!
110 PRINT R$C8,13>
120 END
The expression A$(8,13) identifies the substring of A$ consisting
of six characters starting at the eighth character. If you run the
program, the output will be E. LEE.
■ A$(M,N) gives Mth through Nth characters of A$
String variables can be compared in IF THEN statements. The
comparison is done by alphabetical ordering. Thus A < B since A
comes before B in the alphabet. CAT < DOG, HOUSE > CAR,
PEA < PEARL, and so on.
The last two functions discussed here, CHR$(N) and ASC(A$),
are used to handle the ATASCII standard character set. This set
consists of two-hundred and fifty-six characters numbered 0 through
255. Refer to Appendix C of the ATARI BASIC Reference Manual
for a complete listing of the ATASCII character set.
Characters 0 through 31 have special purposes and are ir¬
relevant here. The numerals 0 through 9 are numbered 48 through
57. The upper-case letters A through Z are numbered 65 through
90. The lower-case letters a through z are numbered 97 through
122. The other numbered characters include punctuation marks,
arithmetic operators ( + , *, etc.), and other special characters.
Two string functions work with the ATASCII character set.
First, CHR$(N) returns the Nth character from the ASCII character
set. For example, CHR$(65) = "A”, CHR$(90) = “Z”, and so forth.
You can also turn things around and convert from a character to
its ATASCII number. This is done with the ASC(A$) function. For
example, ASC(“A”) = 65 and ASC("Z”) = 90.
Suppose that A$ = ''AIRPLANE". What is ASC(A$)? Since
the length of the string is greater than one, only the first character is
considered. In this case the first character is A and ASC(A$) = 65.
String Variables 203
Strings can be joined together (catenated) using the LEN func¬
tion. Thus, for example, if you run the following program
90 DIM A$( 50 >, B$( 50 >
100 LET A$= n HAPPY"
110 LET B$= n GO LUCKY"
120 LET A$< LEN< A$ >+1 )=B$
130 PRINT h$
140 END
it will display
HAPPY GO LUCKY
Each time a string variable is used, it must be dimensioned in a
DIM statement. The DIM should be large enough for the anticipated
number of characters in the string variable.
9-4 PROGRAM EXAMPLES
Example I - String Reversal
The task is to write a program to call for the input of a string and
then print it back in reverse order. Begin with the DIM statement
and the string input.
90 DIM A$< 50 )
100 INPUT h$
The next few lines print the string back in reverse order.
110 FOR X=LEN<A$ > TO 1 STEP -1
120 PRINT h$OT. X);
130 NEXT X
The loop steps backwards from the length of the string to 1. The
function A$(X,X) identifies the substring in A$ consisting of 1 charac¬
ter starting at character number X. This isolates a single character.
204 Hands-on BASIC
With an END statement added the complete program is
90 DIM A$< 50 >
100 INPUT A$
110 FOR X=LENC A$ > TO 1 STEP -1
120 PRINT A$<X,X>;
130 NEXT X
140 END
Try running this program using your own name as input.
Example 2 - Word Count
The number of words in a sentence can be determined from the
number of spaces (assuming that the only purpose of a space is to
separate words). The following program prints out the number of
words in the input string.
90 DIM A$< 50 >
100 INPUT A$
110 LET S=0
120 FOR 1 = 1 TO LENCA$ >
130 IF A$< I, I )<> n " THEN 150
140 LET S=S+1
150 NEXT I
160 PRINT "WORD COUNT = ";S+1
170 END
Study the program until you see exactly how it works. Try out
the program by typing in a sentence. Verify that it works correctly.
Example 3 - Replacement Code
Suppose you want a program to encode a sentence. A simple way to
construct a code (which incidentally could be broken very rapidly
with computers) is to replace each character in the message with
another. This is done most easily by reference to the ATASCII
character set. However, let's do this one “from scratch."
String Variables 205
The first part of the program calls for the DIM statement and
the input of the string to be coded and sets up the conversion scheme.
90 DIM A$< 500 > .■ 30 >, C$< 30 >
100 LET B$="ABCDEFGHIJKLMNOPQRSTUUWXYZ
110 LET C$="ETAUZBHCW KPSYDF,GXIMJLONQU.R"
120 INPUT AS
B$ contains the characters that can be used in the input string
that is to be coded. C$ is the replacement key. An A in the input
string is to be replaced by an E, an F by a B, a ] by a space, and so
on.
Now we can examine each character and do the replacement.
130 FOR 1 = 1 TO LENC AS >
140 FOR J=1 TU 29
150 IF A$< I, I )<>B$( J, J 5 THEN 180
160 PRINT C$< J.• J > J
170 G0TO 190
180 NEXT J
190 NEXT I
The outer I loop steps through each character in AS. The
inner J loop compares the Ith character of AS to the character in BS
until a match is found at the Jth character. When this happens, the
coded Jth character of C$ is printed out, and the program goes on
to the next character in AS.
Finish the program with
200 PRINT
210 END
The complete program is
90 DI M A$< 500 >.. B$< 30 >.. C$< 30 )
100 LET B$="ABCDEFGHIJKLMNOPQRSTUUWXYZ
110 LET C$ ="E T A U Z B H CM K P SYDF,G XIM J L 0N Q U.R"
120 INPUT AS
130 FOR 1 = 1 TO LEN<AS >
140 FOR J=1 TO 29
206 Hands-on BASIC
158 IF A$< I, I J, J) THEN 180
160 PRINT C$< J.* J >
170 GOTO 190
180 NEXT J
190 NEXT I
200 PRINT
210 END
The code can be changed by rearranging the characters in C$.
It might be interesting for you to try out the program and see how
a coded message looks.
9-5 PROBLEMS
1. Write a program that calls for the input of a string and then prints
the string out in a vertical column of characters.
2. If at the input prompt for the program below you type in the string
ABCDEFGH, what will be output?
90 DIM A$< 50 >
100 INPUT A$
110 FOR J=1 TO LEN< AS > STEP 2
120 PRINT A$< J, J>;
130 NEXT J
140 END
3. Write a program to count the number of vowels in an input string.
4. Write a program that calls for the input of a string and then prints
the words in the string in a vertical column.
5. Ask for a sentence to be input. Generate a new string from this
sentence that has all the spaces removed. Then print out the new
string.
6. You want to know how many times each of the twenty-six letters in
the alphabet (you may assume that they are all upper-case) occurs
in ten sentences to be typed in at the keyboard. Do not count spaces
or punctuation marks. Write a program to compute and print out
a table consisting of each of the letters and the number of times it
occurrs in the sentences. Do you think you could identify an author
with the use of such a table?
String Variables 207
7. Assume that five sentences are to be typed in one at a time. Write
a program to count the number of times the word THE appears in
the five sentences.
8. Write a program to count the number of spaces in an input string.
9. Write a program that calls for the input of a string and counts the
number of times the character I is followed by the character N.
9-6 PRACTICE TEST
1. How are string variables identified in BASIC?
2. If A$ = "KITTY” and B$ = "KITTYCAT" then A$ > B$. True or
false?
3. If A$ = "HOW NOW BROWN COW", write a function that will
extract NOW BROWN.
4. Write a program that calls for the input of a string and then keep
printing back the string with one character deleted each time until
nothing is left. If, for example, you typed in PIECE OF CAKE, the
computer should print out
PIECE
OF CA
PIECE
OF CA
PIECE
OF CA
PIECE
OF C
PIECE
OF
PIECE
OF
PIECE
0
PIECE
PIECE
PI EC
PIE
PI
P
208 Hands-on BASIC
5. What will be printed out if you run the following program?
100 FOR N=6 5 TO 90
110 FOR 11=65 TO N
120 PRINT CHRSCM);
130 NEXT M
140 PRINT
150 NEXT N
160 END
CHAPTER 10
SOUND AND
SUBROUTINES
10-1 OBJECTIVES
In this chapter you will learn how the computer can be programmed
to produce sound and perform suboperations. This can be done
through either program segments or special on-line instructions.
Creating Music
In order to create music, you must be able to generate notes.You will
learn to make notes of different intensity and octaves.
Exploring Subroutines
When complicated operations are to be repeated, subroutines are
often very useful. You will learn how subroutines can be set up and
used in BASIC programs.
Working with Program Examples
Sometimes it is difficult for the beginner to see the value of sub¬
routines. You will learn how useful subroutines are as a program¬
ming tool.
10-2 DISCOVERY EXERCISES
1. Turn on the computer and bring up ATARI BASIC. Then type in
the following direct mode statement.
S U U N D 0 ■ 6 8 .» 1 0 .. a
210 Hands-on BASIC
Did you hear anything? If not, turn up the volume on the television
set. If you still do not hear anything, retype the line: You probably
made a typing error when you entered the statement.
2, Now type
SOUND 1,81,10,8
SOUND 2,96,10,8
SOUND 3,121,10,8
How many “voices” do you hear?
L
3. Type
END
What happened?
L
4. Now type the following.
100 INPUT PITCH
110 IF PIT C H =0 THEN 140
120 SOUND 0,PITCH,10,8
1 3 0 G 0 T 0 1 0 0
140 END
Before running the program, think about what will occur. Now rur
the program and eajch time the input prompt is displayed, type ir
one of the numbers in the following sequence: 60, 81, 96, 121, 240
Did the notes get successively higher or lower?
An input of 0 will stop the sound.
Sound and Subroutines 211
5. Clear the program in memory and type in the following.
100 INPUT QUALITY
lie IF QUhLITY=0 THEN 140
120 SOUND 0,121,QUALITY,8
13 0 G 0 T 0 10 0
140 END
Run the program and type in successive numbers from 6 to 19 each
time the input prompt is displayed. What numbers produced sound?
L
6. Now clear the program in memory and type in the following.
100 INPUT LOUDNESS
110 IF LOUDNESS-0 THEN 140
120 SOUND 0,121,10,LOUDNESS
1 3 0 G 0 T 0 1 0 0
140 END
What effect do you think the last of the four numbers in the SOUND
statement has?
Run the program and enter successive numbers from 1 to 16 at each
input prompt. Did the note get louder?
What happened when you entered 16?
Enter 0 to exit the program.
212 Hands-on BASIC
7. Now add the following lines to the program.
121 SOUND 1,60,10,LOUDNESS
122 SOUND 2,81,10,LOUDNESS
123 SOUND 3,36,10,LOUDNESS
and run the program entering the same values as above. What
happened?
8. Now on to something new. Clear the program in memory and enter
the following program:
1 0 0
PRINT
"H"
110
GO SUE:
2 0 0
120
PRINT
li g ii
130
GOSUB
300
140
PRINT
11 j- H
150
END
2 0 0
PRINT
1,
210
RETURN
3 0 0
PRINT
.1
310
RETURN
This program has two statements you haven't seen so far. They
are GOSUB and RETURN. The program itself is intended only to
provide practice in understanding these new statements. Run the
program and record the output.
Compare what was printed out with the program lines that caused
the printout.
9. To which statement does the GOSUB statement in line 110 transfer
the program? (Hint: Look at the table in step 11.)
Sound and Subroutines 213
10. To which statement does the RETURN statement in line 210 transfer
the program? (Hint: Again, examine the table in step 11.)
11. The table below indicates the flow of the program as it is executed.
Line Number What Happens
100
Print out A
110
Transfer to line 200
200
Print out 1
210
Transfer to line 120
120
Print out B
130
Transfer to line 300
300
Print out 2
310
Transfer to line 140
140
Print out C
150
End of program
Study this flow carefully and follow through with the program. Can
you see the purpose of the GOSUB and RETURN statements yet?
What about the placement of the END statement?
12. Clear the program in memory. Enter the following program:
100 REM PROGRAM TO DEMONSTRATE SUBROUTINES
110 DIM 4 >
120 FOR 1=1 TO 4
130 READ A
140 LET %(. I }=A
150 NEXT I
160 REM SORT
17 0 G 0 S U B 4 0 0
180 REM PRINT OUT SORTED ARRAY
190 FOR 1=1 TO 4
214 Hands-on BASIC
200 PRINT X<I>j"
210 NEXT I
220 PRINT
230 LET X< 3 )=7
240 REM SORT AGAIN
250 GOSUB 400
260 REM PRINT OUT SORTED ARRAY
270 FOR 1=1 TO 4
280 PRINT X< I >;
290 NEXT I
300 END
310 DATA 2.-1.-5..6
400 REM SUBROUTINE TO SORT
410 FOR 1=1 TO 3
420 IF XC1+1>>XCI> THEN 470
430 LET C=X<1 + 1 )
440 LET X<1 + 1 >=XC I )
450 LET X<I )=C
460 G0TO 410
470 NEXT I
480 RETURN
Display lines 100 through 200 by typing
LIST 100,200
Check that these lines are correct. Display and check the remaining
lines. This program furnishes an example of how a subroutine might
be used. The subroutine in lines 400 through 480 sorts the array X
into ascending order. Run the program and record the output.
L
Note that the original array is
2 15 6
You can see this by checking the DATA statement in line 310. In line
170, the program jumps to the subroutine, which sorts the numbers.
After the program returns to line 180, the sorted array is now
Sound and Subroutines 215
In line 230, the third element of the array is changed. Line 150
branches the program to the subroutine again for another sorting.
After the return to line 260, the sorted array
1 ^ 6 7
is printed out. Finally, the END command in line 300 stops the
program. Clearly, we could sort the array X as often as desired
merely by inserting a statement GOSUB 400. This is certainly more
efficient that writing out sorting instructions each time they are
needed.
13. Now let us look at another statement. Clear the memory and type
the following program.
100 PRINT "ENTER h NUMBER BETWEEN 1 AND 5"
110 PRINT "ENTER 5 TO QUIT."
120 COLOR 1
138 INPUT N
1 40 ON N GOSUB 1 000.. 2000.« 3000 .« 4000
150 IF H=5 THEN END
160 GOTO 100
1 0 0 0
GRAPHIC
S 8
1 0 1 0
PLOT 5,
5 : DRAWTO 20,5
1 0 2 0
DRAWTO
20,20 : DRAWT0 5,5
1 0 3 0
RETURN
2 0 0 0
GRAPHIC
S 8
20 1 0
PLOT 5,
5 : DRAWTO 50,5
2020
DRAWTO
50, 20:DRAWTO 5,20
2 0 3 0
DRAWTO
ET CT
• J .« J
2040
RETURN
3 0 0 0
GRAPHIC
«“- i~>
3 0 1 0
PLOT 5,
50 : DRAWTO 5,5
3 0 2 0
DRAWTO
3 0,5 : D R A W T 0 3 0,2 0
3 0 3 0
DRAWTO
5,20
3040
RETURN
4 0 0 0
GRAPHIC
•-* O
4010
PLOT 50
,0=DRAWTO 0,0
4020
DRAWTO
30,10 : DRAWTO 0,20
4 0 3 0
RETURN
216 Hands-on BASIC
What figure will be drawn if you enter 3?
Run the program. Were you right?
L
Input in the other choices to see what is drawn. Input 5 to quit.
14. This completes the computer work for this chapter. Turn off the
computer.
10-3 DISCUSSION
Creating Music
The SOUND statement instructs the computer to play notes. The
four numbers that follow the SOUND statement allow for the varia¬
tion in the notes played. The first number indicates which “voice”
is to be used. The four voices available are numbered 0 through 3.
As you saw in the discovery exercises, the effect of harmonizing can
be attained by using all four voices at the same time.
The second number indicates what note will be played. A
value of 121 will play the musical note middle C. A value of 60 will
also play a C note except that it will be one octave higher, while a
value of 243 will play a C note that is one octave lower than middle
C. A list of numbers and their corresponding notes can be found in
Table 10.1 of the ATARI BASIC Reference Manual.
The third number refers to the quality of the note being played.
Essentially, there are two qualities of notes —“pure” tone and dis¬
tortion. Distortion allows you to produce sound effects. Values of
10 and 14 produce “pure” tones, while other even values produce a
variety of distortions. Odd values produce silence.
The fourth number determines how loud the note will be;
the higher the number, the louder the note. Thus the direct mode
statement
SOUND 2,121,10,8
produces a middle C note in voice 2 with a “normal” loudness.
Use the SOUND statement to play music on the computer.
Sound and Subroutines 217
Exploring Subroutines
You will almost certainly encounter complicated situations in which
you want to carry out the same process many times in a program.
Subroutines are very useful for this purpose. The diagram below
indicates how a subroutine might be used in a program.
Main program begins _____
2 0 0 G O S U B 1 0 0 0
210
350 GQSUB 1000
3 b Ei
Main program ends 430 END
Subroutine begins 1 0 0 0 R E M SU B E O U TINE
End of subroutine 1150 RETURN
When the computer reaches the GOSUB in line 200 of the
program above, it jumps to line 1000 and executes the subroutine
beginning on that line. When the computer encounters the RETURN
in line 1150, it goes back to line 210, the next higher line number
after the GOSUB that put it in the subroutine. Then the computer
proceeds through the main program until it reaches the GOSUB in
line 350, where it again branchs to the subroutine in line 1000. This
time the RETURN statement directs the computer back to line 360.
Of course, you can use GOSUB 1000 as many times as you
want in this program or can have as many subroutines as you need.
218 Hands-on BASIC
Generally, the main program is at the beginning and the subroutines
are grouped together at the end. There is a good reason for this. The
subroutines are performed only when they are called by a GOSUB.
After the main program is finished, put an END statement in the
program.
■ Transfer to subroutines with GOSUB.
It is possible, and sometimes desirable, to jump to a subroutine
from a subroutine. The diagram below indicates how the computer
treats such an event.
Main program
_Subroutine 1
4 Ei 0 G 0 S U B 8 0 0 —► 8 0 8
410
_ Subroutine 2
8 2 0 G 0 S U B 9 0 0 —► 9 0 0
830 ◄-i-
550 END
■— 880 RETURN
I— 990 RETURN
Note that the computer jumps from 400 to 800, then from
820 to 900, and finally arrives at the RETURN in line 990. But
where does the RETURN direct the computer—to line 410 or to line
830? The rule is that the RETURN directs the computer back to
the next statement after the GOSUB that put it in the subroutine
containing the RETURN. The computer is in subroutine 2 because
of the GOSUB in line 820; hence the RETURN in line 990 directs it
back to line 830. The same rule applies to the RETURN in line 880.
At that point the computer is in subroutine 1 and arrived there from
the GOSUB in line 400. Thus, the RETURN in line 880 directs the
computer back to line 410.
Sound and Subroutines 219
■ Get back from subroutines with RETURN
The ON...GOSUB statement allows you to direct the computer
to one of numerous subroutines, depending on the value of a numeric
variable. For example, the statement
140 OH N GOSUB 300,400,500
will go to the subroutine at 300 if N is 1, to the subroutine at 400
if N is 2, or to the subroutine at 500 if N is 3.
At this point it may not be clear to you why subroutines are
valuable. The need for subroutines becomes more evident as you
acquire more skill as a programmer. For the moment, remember
that subroutines are one of the most valuable tools available to the
programmer.
10-4 PROGRAM EXAMPLES
Example 1 - Waiting a Song
To compose music on the computer, you need to know what numbers
play which notes and how to insert pauses. A simple FOR NEXT
loop can accomplish this. The READ DATA statements are the most
useful for producing songs. Start with the loop to generate the notes
and pauses as follows:
100 FOR K=1 TO 54
110 READ PITCH,LENGTH
120 FOR L=1 TO LENGTH
130 SOUND 0,PITCH,10,8
140 NEXT L
150 NEXT K
This is the heart of the program because the inner FOR NEXT loop
plays the desired note for the length of time given by the variable
LENGTH. You can insert pauses easily by using a value that produces
silence. You compose the song by choosing appropiate notes and
pauses.
220 Hands-on BASIC
The complete program for the song Row, Row, Row Your
Boat follows.
100 FOR K=1 TO 54
110 READ PITCH.. LENGTH
120 FOR L=1 TO LENGTH
130
SOUND
0 .«
PIT C
H
..
10 , 8
140
NEXT
L
150
NEXT
K
160
DATA
121
, 50
..
0
..
5,121
.
50
0
c
t ._!
170
DATA
121
.« 30
..
0
..
2, 188
..
15
0
.* 2
180
DATA
96..
6 0..
0
5
. 96 . 5
0
.* 0
2
198
DATA
108
20
0
2.. 96..
cL
0..
0
..
10
2 0 0
DATA
91,
2 0 «
8
5
,81,100,
0
..
10
210
DATA
6 0..
15,
0
.-•*
, 60.. 1
cr
-_i
.« 0
2
220
DATA
6 0 .■
15,
0
2
, 81 , 1
tr
._!
0
2
230
DATA
81 ,
15,
0
2
, 81, 1
cr
-_i
.« 0
..
2
240
DATA
96 .«
15,
0
2
, 96, 1
cr
._i
.« 0
2
250
DATA
96 .«
15,
8
2
,121,
1
cr
._! .«
0
..
2
2 6 0
DATA
121
, 15
.*
8
..
2,121
..
15
0
.• 2
270
DATA
81 ,
2 5 .«
0
5
,91,1
cr
_i
.. 0
..
2
2 8 0
DATA
96 ..
-“« cr
cL .*
0
cr
, 108,
2
0 .«
0
..
“7
290
DATA
121
-“« cr
.« .il J
0
,
cr
300 END
Note that you won't know the value of 54 in line 100 until you know
how many READ statements you will need to program the song.
Example 2 - Rounding off Dollar Values to Cents
Business applications generally involve printing out the results of cal¬
culations in dollars and cents. Since the computer normally handles
nine significant figures, it is not unusual for the computer to type
23.1579384 and similar amounts. Ordinarily, you would want to
round off the figure to the nearest cent, or 23.16.
You can use a subroutine to round off the numbers. Let's write
a program that will produce the following output when executed:
L h B E L PRICE ? (You type in price)
10"; DISCOUNT IS (Computer prints discount price)
15"; DISCOUNT IS (Computer prints discount price)
20"; DISCOUNT IS (Computer prints discount price)
Sound and Subroutines 221
All dollar values typed out should be rounded off to the nearest cent.
First set up a method to do the rounding off. A subroutine to
accomplish this is
3 0 0 Y = IN T C X + 10 0 + . 5 ) 1 0 0
310 RETURN
To see how this expression works, suppose X = 23.1597. Follow
this value through the expression to see what happens.
X*100
2315.97
X *100+0.5
=
2316.47
INT(X*100 + 0.5)
=
2316
INT(X*100 + 0.5)/100
=
23.16
Therefore, 23.1597 was correctly rounded “up” to 23.16.
But suppose that X — 23.1547.
X*100
=
2315.47
X*100 +0.5
=
2315.97
INT(X*100 + 0.5)
=
2315
INT(X*100+ 0.5)/100
=
23.15
the computer rounds 23.1547 “down” to 23.15.
The first few lines of the program are self-explanatory.
100 PRINT "LABEL PRICE 11
110 INPUT Z
To obtain the first discount rounded off to the nearest cent,
use the following subroutine:
120 LET X=0.9*Z
130 GOSUB 300
140 PRINT "10V DISCOUNT IS "iV
222 Hands-on BASIC
The remaining discount prices are determined in the same way.
The complete program is
1 00
PRINT "LABEL PRICE";
110
INPUT Z
120
LET K=Q.3tZ
130
G 0 S U E: 3 0 0
140
PRINT "10’i DISCOUNT
IS "
150
LET X=0.85*Z
160
G 0 S U B 3 0 0
170
PRINT "15‘-. DISCOUNT
IS "
180
LET H=0.8*Z
190
G 0 S U B 3 0 0
2 0 0
PRINT "20V DISCOUNT
IS "
210
END
3 0 0
Y=INTC X*100+.5>/l00
310
RETURN
In lines 130, 160, and 190 the rounding-off subroutine is
called and used. If the discount is 10 percent, the selling price is
90 percent of the original price, Z. Thus, the computer calculates
0.9*Z, which is rounded off to the nearest cent in the subroutine.
Example 3 - Carpet Estimating
Suppose you want to write a program that uses a subroutine to
compute the price of installed carpet. There are four grades of
carpet, and each is discounted as the quantity of carpet ordered
increases. Assume that the price structure is as follows:
1
2
3
A
$10.00
$ 8.50
$ 7.25
B
13.25
12.00
9.75
Grade
C
16.00
14.00
11.25
D
20.00
17.20
15.25
The rows represent the four grades of carpet. The numbers at the
top of the columns represent quantities installed, as follows:
Sound and Subroutines 223
1. First 15 square yards
2. Any part of the order exceeding 15 but not more than 25 square
yards
3. Anything over 25 square yards
When executed, the program should produce the following output:
HON MANY ROOMS? (You type in)
FOR EACH ROOM, TYPE IN LENGTH
AND WIDTH IN FEET SEPARATED
B Y A C 0 M M A
ROOM DIMENSIONS
1 (You type in)
2 (You type in)
(Loop until all rooms are entered)
(Computer types out number) SQU ARE V A R DS R E0U I R E D
CARPET GRADE COST OF ORDER
A (Computer types out,etc.)
B
C
D
Before getting involved in the program, think a bit about the
output. Since the output is in dollars and cents, you can use the
subroutine in example 2 to round off the answers. The first few
lines follow without difficulty.
1 0 0
PRINT
"HOW
MANY ROOMS ">
110
INPUT
N
120
PRINT
"FOR
EACH ROOM, TYPE IN LENGTH"
130
PRINT
"AND
WIDTH IN FEET SEPARATED"
140
150
PRINT
PRINT
"BY f
-i COMMA"
160
170
PRINT
PRINT
"Roor
1" , "DIMENSIONS"
You are ready to call for the input of the room dimensions.
Use the variable A to keep track of the area of the rooms. Remember
that the area of a room is its length times its width.
224 Hands-on BASIC
130 LET 3=0
190 FOR 1=1 TO N
200 PRINT I,
210 INPUT L,W
220 LET A=A+L*W
230 NEXT I
Since the total room area is now in square feet, include pro¬
gramming instructions to divide the area by 9 to convert to square
yards, and then to print out the quantity of carpet required.
240 LET A = A9
250 PRINT A.;" SQUARE YARDS REQUIRED"
At this point include the price table in the program in the form
of DATA statements.
2 b 0 DATA 10 , 8.5 > 7.2 5
270 DATA 1 3.2 5.. 1 2 .. 9.7 5
280 DATA 16,. 14,11.25
290 DATA 20,17.2,15.25
Next print out the heading required for the price printout.
300 PRINT
310 PRINT "CARPET GRADECOST OF ORDER"
320 PRINT
Now you come to the point in the program where the sub¬
routine will be useful. Since you don’t know precisely where the
subroutine should begin, simply use a large line number and correct
it later if needed.
330 REM COMPUTE PRICE FOR GRADE A
3 4 0 G 0 S U Ei 8 0 0
Let’s write the subroutine now. First, for each of the grades
of carpet you need the three prices. Use a READ statement to get
the prices from the DATA statements.
800 REM SUBROUTINE TO COMPUTE CARPET PRICE
810 READ C1,C2,C3
Sound and Subroutines 225
Next the program should determine if the area of the carpet
is less than 15, between 15 and 25, or more than 25 square yards
and then compute the price accordingly.
820 IF A>25 THEN 860
830 IF h > 15 THEN 380
840 LET P=C1*A
8 5 0 G O T 0 8 9 0
860 LET P=15*Ci+10*C2+<A-25>*C3
870 GOTO 89Ei
880 LET P = 15£C1 + C A -15>#C2
8 9 0 G 0 S U B 1 0 0 0
900 RETURN
Study this program segment to convince yourself that the price
is being computed correctly. Note how the rounding off subroutine
is called within this subroutine. Now return to the main program
and add a statement to print out the first price.
350 PRINT 11 A 11 .« Y
Once you establish this pattern, the rest of the main program
follows easily.
3 6 Ei
REM C
OMPIJTE
370
GOSUB
8 0 0
3 8 0
PRINT
I! 0 it y
398
REM C
OMPIJTE
4 Ei 0
GOSUB
8 0 0
410
PRINT
" C " , Y
420
REM C
OMPIJTE
430
GOSUB
8 8 0
440
PRINT
" D " , Y
450
END
PRICE FOR GRADE B
PRICE FOR GRADE C
PRICE FOR GRADE D
You need the END statement in line 450 to prevent the program
from falling into the subroutine.
The subroutine, as you see, saves programming time and
makes programs shorter. If you rewrote this program without
GOSUBs, you would need to add many statements at each point
the GOSUB is used.
226 Hands-on BASIC
The complete program is
1 0 0
110
120
130
140
150
160
170
180
1 90
2 0 0
210
220
230
240
250
260
270
2 8 0
2 9 0
300
310
320
330
340
350
360
3 7 0
3 8 0
390
400
410
420
430
440
450
8 0 0
81 0
820
830
PRINT "HOW MANY ROOMS"
INPUT H
PRINT "FOR EACH ROOM, TYPE IN LENGTH"
PRINT "AND WIDTH IN FEET SEPARATED"
PRINT "BY A COMMA"
PRINT
P R IN T " R 0 0 M " , " D I M E N S 10 N S "
PRINT
LET A=0
FOR 1=1 TO N
PRINT I,
INPUT L,W
LET A=A+L*W
NEXT I
LET A = A /9
PRINT Aj" SQUARE YARDS REQUIRED"
DATA 10,8.5,7.25
DATA 13.25,12,9.75
DATA 16,14,11.25
DATA 20,17.2,15.25
PRINT
PRINT "CARPET GRADE","COST OF ORDER"
PRINT
REM COMPUTE PRICE FOR GRADE A
GOSUB 800
PRINT "A",Y
REM COMPUTE PRICE FOR GRADE B
GOSUB 800
PRINT "B",Y
REM COMPUTE PRICE FOR GRADE C
GOSUB 800
PRINT "C",Y
REM COMPUTE PRICE FOR GRADE D
GOSUB 800
PRINT "D",Y
END
REM SUBROUTINE TO COMPUTE CARPET PRICE
READ Cl,C2,C3
IF A>25 THEN 860
IF A>15 THEN 880
Sound and Subroutines 227
840 LET P=C1*A
850 GOTO 890
860 LET P=15*Cl+10*C2+<A-25)*C3
870 GOTO 890
880 LET P=15*Cl+<A-15)*C2
890 GOSUB 1000
900 RETURN
1000 LET Y=INT<P*100+.5VI00
1010 RETURN
Example 4 - Designing a House
This program draws a house. The subroutines in the program
use the graphics statements we introduced in Chapter 3. As you read
this program example, pay close attention to the REM statements.
The instructions, set up, and GOSUBs to draw the parts of the house
are at the beginning of the program. The subroutines begin in line
1000 .
You draw the roof first. You select the roof position using the
POINT MOVING program you studied in Chapter 6, step 15. You
position the roof by moving the point to the location you wish using
the L, R, U, and D keys.
You draw the frame next and make decisions about the win¬
dows and the door. Notice that the roof drawing subroutine (line
1000), window drawing subroutine (line 3000), and door draw¬
ing subroutine (line 4000) use the POINT MOVING program (line
5000) as a subroutine. Note that, except for the roof, each object is
drawn using the subroutine in line 7000. Recall that after you posi¬
tion the point on the screen with the POINT MOVING program,
you exit by typing a Q.
If you wish to enter and run this program, you may save
yourself some typing by loading the POINT MOVING program you
saved in Chapter 6 step 15 and and changing the numbering so it
begins at line 5000. Note the small modification to this program
in the listing of the complete program which follows. Again, do
not become concerned with the statement in line 110 as it will be
discussed fully in the last chapter.
228 Hands-on BASIC
1 0 0
REM
DESIGNING h HOUSE
110
OPEN #1,12,0,"K ="
120
DIM AN
S$< 20 ), Y$< 1 ), ARRA YC 10.
2 > .* SC 10.- d
130
PRINT
"YOU CAN MOUE THE POINT ON THE'
140
PRINT
"SCREEN TO LOCATE THE
BOTTOM"
150
PRINT
"CENTER OF THE ROOF,
WINDOWS,"
160
PRINT
"AND DOOR ON THE HOUS
E. PRESS"
170
PRINT
"U,D,L,R TO MOUE THE
POINT"
180
PRINT
"ON THE SCREEN. WHEN
YOU HAUE"
190
PRINT
"THE POINT WHERE YOU
WANT IT,"
2 0 0
PRINT
"PRESS Q."
210
PRINT
220
PRINT
"ENTER SCALE FACTOR <
1 TO fa ) ."
230
INPUT
SCALE
240
GRAPHICS 8
250
COLOR
1
260
REM DRAW ROOF
270
GOSUB
1 0 0 0
280
REM DRAW HOUSE FRAME
290
GOSUB
2 0 0 0
300
REM DRAW WINDOW
310
GOSUB
3 0 0 0
320
REM DRAW DOOR
330
GOSUB
4 0 0 0
340
END
1000 REM ROOF DRAWING SUBROUTINE
1010 REM GOSUB POINT MOWING SUBROUTINE
1020 G 0 S U B 5000
1030 REM GOSUB ARRAY READ AND
1040 REM SCALE SUBROUTINE
1050 LET N00FF'TS = 5
10 fa 0 G 0 S U E: 6 0 0 0
1070 PLOT A.. B : DRAWTO A+S< 1,1), B + SC 1,2)
1 O S 0 F 0 F! R=2 T U 5
1090 ElF! hWTO A + SR, 1 ), E: + SC F!, 2 )
1100 NEXT R
1110 PLOT A,B
1120 DATh 0,0,15,0,0,-5,-15,0,0,0
1130 RETURN
2000 REM FRAME DRAWING SUBROUTINE
2010 REM GOSUB ARRAY READ AND
Sound and Subroutines 229
2020 REM SCALE SUBROUTINE
2038 LET NOOFFTS=6
2 0 4 0 G 0 S U B 6 0 0 0
2050 REM GOSUB DRAW THE OBJECT SUBROUTINE
2 0 6 0 G 0 S U B 7 0 0 0
2070 DATA 0,0,-15,0,-15,10,15,10,15,0,0,0
2 ti B O F! E TIJ E! N
3000 REM WINDOW DRAWING SUBROUTINE
3010 LET N00F P T S=6
3020 REM GOSUB ARRAY READ AND
3030 REM SCALE SUBROUTINE
3 0 4 0 G 0 S U B b 0 0 0
3050 PRINT "DO YOU WANT WINDOWS? < Y- N >"
3060 INPUT ANSI
3070 IF ANS$< >"Y” THEN 3170
3080 REM GOSUB POINT MOWING SUBROUTINE
30 9 0 G 0 S U B 5 0 0 0
3100 REM GOSUB DRAW THE OBJECT SUBROUTINE
3110 G 0 S IJ B 7 0 0 0
3120 PLOT A,B
3130 DATA 0 , 0 , 1 , 0 , 1 ,- 3 ,- 1 ,- 3 , - 1 , 0 , 0 , 0
3140 PRINT "ANOTHER WINDOW? <Y--N>"
3150 INPUT ANSS
3160 IF ANS$="Y" THEN 3090
3170 RETURN
4000 REM DOOR DRAWING SUBROUTINE
4010 LET N00FPTS = 6
4 0 2 0 R E M G 0 S UB A R R A Y READ A ND
4030 REM SCALE SUBROUTINE
4 0 4 0 G 0 S U B 6 0 0 0
4050 F' R IN T " D 0 Y 0 U W ANT A D 0 0 R ? < YN > "
4060 INPUT ANSI
4070 IF ANS$< >"Y" THEN 4150
4080 REM GOSUB POINT MOOING SUBROUTINE
4 0 9 O G 0 S U B 5 0 0 0
4100 REM GOSUB DRAW THE OBJECT SUBROUTINE
4110 G 0 S U B 7 0 6 0
4120 PLOT A,B
4130 DATA 0 , Hi ,1.5,0, 1.5,-5
4 1 40 DAT A -1.5,-5 , -1 .5,0,0,0
4150 RETURN
230 Hands-on BASIC
5000 REM POINT MOWING SUBROUTINE
5010 LET A=160
5020 LET B=96
5030 REM PLOTS A WHITE POINT AT <A,B >
5040 COLOR 1
5050 PLOT A,B
5060 GET #1,X
5070 LET Y$=CHR$< X >
5080 REM PLOTS A BLACK POINT AT <A,B>
5 Hi 9 0 C 0 L 0 R 0
5100 PLOT A,B
5110 IF Y$="D" THEN B=B+5
5120 IF Y$="U" THEN B = B-5
5130 IF Y$="L" THEN A=A-5
5140 IF Y$="R" THEN A=A+5
5150 IF Y$="Q" THEN 5170
5160 G 0 T 0 5 0 4 0
5170 COLOR 1
5180 RETURN
6000 REM ARRAY READ AND
6010 REM SCALE SUBROUTINE
6020 FOR R = 1 TO NOOFF'TS
6030 FOR C=1 TO 2
604 0 READ W
6050 LET A R R A Y < R.. C >=W
6060 LET S< R.. C )=S C A L E $ A R R A Y < R .. C >
6070 NEXT C
6080 NEXT R
6090 RETURN
7000 REM DRAWING THE OBJECT SUBROUTINE
7010 PLOT A,B■DRAWTO A + S<1,1),B+St1,2 >
7 o 2 0 F U R F! = S' T U 6
7030 DRAWTO A+S< R .■ 1 > .. B + S( R .. 2 >
7040 NEXT R
7050 RETURN
Note: You must be careful where you move the starting point
for the house so that lines drawn do not go off the screen. If the
program does attempt to draw lines that go off the screen, you will
get an error message and you will need to rerun the program.
Sound and Subroutines 231
10-5 PROBLEMS
1. The following sequence of pitch values are for the song Frere Jacques.
Use them and appropriate pauses to play the song. The grouping is
for convenience.
121 .. 108 , 96 , 121 , 121 , 108 , 96 , 121 ,
96 , 91 , 81 , 96 , 91 , 81 ,
81 . 72 . 81 . 91 . 96 . 121 , 81 , 72 , 81 , 91 , 96 , 121 ,
121 . 162 . 121 , 121 , 162,121
2. What will be output by the following program?
100 DIM A<5>
110 FOR 1=1 TO 5
120 REA D X
130 LET A<I>=H
140 NEXT I
150 DATA 6,2,7,1,3
1 6 0 G 0 S U B 5 0 0
170 LET A< 3 >=10
18 0 G 0 S U B 5 0 0
190 LET A<5> = 8
2 0 0 G 0 S U B 5 0 0
210 END
500 FOR 1=1 TO 4
510 LET AC I :'=AC 1 + 1 >
520 NEXT I
5 3 0 G 0 S U B 6 0 0
540 RETURN
6 0 0 F 0 R J = 1 T 0 5
610 PRINT AC-J;.,
620 NEXT -J
630 RETURN
3. What will be printed if you run the program below?
100 LET X =10
110 GOSUB 500
120 PRINT S
130 LET X=X^2
232 Hands-on BASIC
140
GO SUB
150
PRINT
160
LET X=
170
G0SUB
180
PRINT
190
END
5 0 0
LET S=
510
FOR Y =
520
LET S=
530
NEXT Y
540
RETURN
4. Assume that a one-dimensional array Z contains numbers to be
added together. The first element of the array Z(l) gives the number
of elements that follow in the array and are to be summed. Write
a subroutine beginning in line 800 to compute the sum of the ele¬
ments after Z(l). Assign the sum to the variable T. Terminate the
subroutine with a RETURN statement. Assume that the array Z has
been properly dimensioned and that the values in the array have
been loaded in the main program.
5. X is a one-dimensional array. The first element of the array X(l)
gives the number of pieces of data that follow in the array. Write
a subroutine beginning in line 500 to search through that array for
the largest value. Assign this value to the variable L. Terminate the
subroutine with a RETURN statement. Assume that the array X has
been properly dimensioned and loaded with numbers elsewhere.
6. Suppose that as part of a printout you need a series of seventy-two
* characters in a straight line across the page. Write a subroutine
beginning in line 1000 to do this. Terminate the subroutine with a
RETURN statement.
7. Assume that a one-dimensional array Y is loaded with numbers. The
first element Y(l) gives the number of elements to follow. We want
a subroutine to calculate the mean (M) and standard deviation (S)
of the numbers in the array that follow the first element. Begin the
subroutine in line 900 and terminate with a RETURN statement.
The formulas for calculation of the mean and standard deviation
are given below.
Mean = (Sum of values)/N
Sound and Subroutines 233
Standard
deviation
Nxfsum of squares of values) — (sum of values) 2
Nx(N - 1)
10-6 PRACTICE TEST
1. Which note will be lower when the following direct mode statements
are entered?
S 0 U N D 0 ..96.* 10 , S
SOUND 8, 162, 10,8
2. How do you pass control from the main program to the subroutine?
How do you pass control from the subroutine back to the main
program?
What will be printed
out if you run the following program?
1 0 0
LET 0 =
i
110
GOSUB
2 0 0
120
LET 0 =
A + 4
1 30
GOSUB
2 0 0
140
LET 0 =
P-2
150
GOSUB
2 0 0
160
END
2 0 0
REM SU
BROUTINE
210
IF 8< 2
THEN 250
2 2 0
IF 0 = 3
THEN 270
230
PRINT
"RED"
240
GOTO 2
8 0
250
PRINT
"WHITE"
260
G 0 T 0 2
8 0
270
PRINT
"BLUE"
280
i_
RETURN
CHAPTER 11
RANDOM NUMBER
AND SIMULATIONS
11-1 OBJECTIVES
One of the most interesting applications of computers concerns
simulation of events or processes that involve an element of chance.
For instance, the computer can simulate gambling games or inves¬
tigate the number of bank tellers required to ensure that arriving
customers do not have to wait more than a few minutes to be served.
In this chapter we will see how the computer can be used to handle
problems of this type.
Generating Random Numbers
Your ATARI computer has a random-number generator function
that is the heart of all programs involving the element of chance, or
randomness. You will learn how these random-number generators
can be employed in BASIC programs.
Designing Sets of Random Numbers
Sometimes you will need a set of random numbers with characteris¬
tics of your own choosing. You will learn how to get the computer
to generate numbers in a set you define.
Working with Program Examples
Your programming work in this chapter will involve simulations and
applications that involve the element of chance.
236 Hands-on BASIC
11—2 DISCOVERY EXERCISES
Setting up the Random-Number Generator
By their very nature, random-number generators produce sequences
of numbers that appear to have no pattern or relationship. If a
random-number generator is to be useful, it must produce a a dif¬
ferent sequence of numbers each time it is used in a program.
1. Turn on the computer and bring up ATARI BASIC.
2. Enter the following program:
1 0 0
FOR I
= 1 TO 9
110
PRINT
RND< 0 )
120
NEXT
I
130
END
Run the program. Record the largest and smallest numbers that were
printed out.
3. Run the program again. Did the same numbers appear?
What was the largest number typed out?
i_
What was the smallest number?
4. Change line 110 as follows.
110 PRINT RHD<-1>
Run the program several times. Were all the numbers different?
Random Numbers and Simulations 237
Change line 110 as follows.
110 PRINT RND< 52 >
Run the program. Were all the numbers different?
5. Clear the program in memory. Enter the following program:
100 LET L=.5
110 LET S=.5
120 FOR 1=1 TO 100
130 LET X=RND<0>
140 IF X>L THEN 170
150 IF X<S THEN 190
1 6 0 G 0 T 0 20 0
170 LET L = X
180 GOTO 200
190 LET S=X
200 NEXT I
210 PRINT "LARGEST = " L
220 PRINT "SMALLEST = ";S
230 END
This program examines all the numbers generated by the RND func¬
tion and keeps track of the largest and smallest numbers generated.
As the program stands, it will generate 100 random numbers. Run
the program and record what was typed out.
L
6. Type
120 FOR 1=1 TO 1008
Now the program will generate 1000 random numbers. Run the
program and record what was printed out. Be prepared to wait
about 25 seconds for the output.
238 Hands-on BASIC
Based on what you have seen thus far, what do you think is the
largest number that the RND function will generate?
What about the smallest?
7. Now let's go on to some other ideas associated with random num¬
bers. Clear the program in memory and enter the following pro¬
gram:
100 FOR 1=1 TO 10
110 PRINT INT(2*RND<0)>
120 NEXT I
130 END
Run the program and record the output.
L
What were the only two numbers typed out?
8. Type
110 PRINT INK 3*RND< 0 >>
Display the program. If you run this program, what numbers do
you think will be typed out?
Can you predict anything about the sequence or pattern in which
the numbers will be typed out?
Random Numbers and Simulations 239
9. Type
110 PRINT INK 2*RHD03 )+l >
What do you think the program will do now?
Run the program and record the output.
10. Type
110 PRINT INK 4*RN0< 0 > + 4 )
If you run the program, what do you think will be printed out?
Run the program and describe the output.
Is there a pattern in the output?
11. Type
110 PRINT INT<30*RND<0>K10
Display the program and study it carefully. What do you think this
program will print out?
Run the program and describe the printout.
240 Hands-on BASIC
12. Type
110 PRINT I NT C 200XRNDC 0 > > •*' 100
Display the program in memory. What do you think will happen if
you run this program?
See if you were right. Run the program and record the output.
L
13. Turn off the computer. This terminates the computer work for now.
11-3 DISCUSSION
Generating Random Numbers
The details of how random numbers are generated are not important
here; it is enough to say that several mathematical methods can be
used to produce these numbers. Remember, however, that the RNC
function calls on the random-number generator. This function is
used like the other built-in functions of BASIC that you studied
previously, but differs in one important respect.
Recall that the argument of a function (what the functior
works on) determines the result. Thus, SQR(4) is 2, INT(3.456'
is 3, and so forth. The RND function also requires an argument bui
seems to use no logical rules to generate numbers. Of course, this
randomness is precisely the point of the function.
The function generates numbers between 0 and 1 at random
All the numbers in the interval have an equal chance of showing up
Actually, the range of numbers generated is from 0.0000000000 tc
0.9999999999. Zero can show up occasionally, but the number 1
never occurs.
■ RND function generates numbers in the range 0 to .9999999999.
Random Numbers and Simulations 241
Designing Sets of Random Numbers
Most often the random numbers in the range produced by the RND
function are not the most useful. More typically, programs call for
random integers (whole numbers) over a certain range or a set of
random numbers with a particular set of characteristics. Therefore,
it is useful to learn how to generate sets of random numbers with
characteristics you can specify.
Let's begin with the characteristics of the RND function. RND
delivers numbers in the range 0 to 1, that is, from 0 to slightly less
than 1. If you multiply RND by N, you multiply the range of the
function by N. Thus, N*RND(0) produces random numbers in the
range 0 to N. If you wish, you can shift the numbers (keeping the
same range) by adding a number. N*RND(0)+A produces random
numbers over the range A to (A + N) or from A to slightly less than
(A + N). Also, you can take the integer part of an expression, using
the INT function, to produce random integers. The table below
shows how the RND function might be used.
BASIC Expression
5*RND(0) + 10
INT(5*RND(0) + 10)
INT(2*RND(0) + 1)
100*RND(0)
Result
Random numbers in the range 10 to 15
Random integers 10, 11, 12, 13, 14
Random integers 1, 2
Random numbers in the range 0 to 100
You may have encountered the notion of mean and standard
deviation (see problem 7 in Chapter 10). You can use the RND
function to generate numbers that appear to be drawn from a col¬
lection of numbers having a given mean and standard deviation. The
rule for generating these numbers is
X = M + S((sum of 12 numbers from RND function) — 6)
where M and S are the desired mean and standard deviation, respec¬
tively. The values of X will appear to come from a collection of num¬
bers with mean M and standard deviation S. The values of X would
fall along the bell curve that you have probably seen in textbooks.
A subroutine would be very useful in this application.
242 Hands-on BASIC
11-4 PROGRAM EXAMPLES
The following examples illustrate how random numbers can be used.
Study these examples carefully and make sure you understand ex¬
actly what is taking place.
Example 1 - Flipping Coins
One of the easiest applications of random numbers is a coin-tossing
simulation. The goal is to write a program that will produce the
following printout:
TOSS
1
4
etc
The outcome is to be determined randomly for each toss of
the coin, with both heads and tails having equal probability. The
program should print out the results of ten coin tosses.
The first part of the program generates the heading and the
space indicated in the printout above.
1 00 PR I NT "TOSS 11 , " OUTCOME"
110 PRINT
Now open the loop to generate the ten tosses of the coin.
120 FOR 1 = 1 T 0 10
The next step is to generate Os and Is randomly. Assume that
a 0 signifies heads and a 1 signifies tails. You should be able to
convince yourself that the following statement will produce Os and
Is randomly.
130 LET X= I NT< 2:fcRND< 0 > >
OUTCOME
H
T
T
H
Random Numbers and Simulations 243
Now analyze X to see whether heads (0) or tails (1) has come up.
140 IF X = 0 THEN 170
150 PRINT Ii'T
160 GOTO 180
170 PRINT I/'H"
180 NEXT I
All that remains now is the END statement.
190 END
The complete program is listed below.
100 PRINT “TOSS","OUTCOME"
110 PRINT
120 FOR 1=1 TO 10
130 LET X=INT<2*RND<0)>
140 IF X=0 THEN 170
158 PRINT L"T"
1 b 0 G 0 T 0 1 8 0
170 PRINT I,"H"
180 NEXT I
190 END
Run this program several times and count the number of tails
and heads that show up.
Example 2 - Random Integers
The next problem is to write a BASIC program to generate and
print out 50 random integers (whole numbers) over the range 10 to
15. The only part of the program that requires much thought is the
statement to generate the random integers, so concentrate on this
one statement.
Remember that RND generates numbers over the range 0 to 1.
Thus, 6*RND(0) will generate numbers in the range 0 to 6. Actually
the upper limit is 5.99999999. By using the integer function, you
can convert from random numbers to random integers. INT(6*RND)
will produce the integers 0, 1, 2, 3, 4, 5 randomly. To get integers
in the range 10 to 15, you must add 10. Thus, the expression
INT(6*RND(0)) + 10 will produce the desired numbers.
244 Hands-on BASIC
Once this line is figured out, the program follows easily.
100 FOR 1=1 TO 50
110 LET Y=INT< b#RND< 8 >>+10
120 PRINT Y; 11 ” ;
138 NEST I
140 END
Example 3 - Distribution of Random Numbers
Suppose you generate a great number of integers at random over the
range 1 to 10. If the random-number generator on the computer is
working properly, you would expect to get the same number of each
of the integers. If you generated 1000 integers, you would expect to
get 100 Is, 100 2s, and so on. The problem is to write a BASIC
program that tallies the random integers as they are generated and
then prints out the totals. These totals will tell you how well the
computer's random-number generator is working.
First, think about how you are going to do the tally. A good
way to do this is to use a one-dimensional subscripted array. X(l)
will contain the number of Is generated, X(2) the number of 2s, and
so forth up to X(10). Thus, the first task is to dimension the array
and set all the values in the array equal to 0.
100 DIM X< 10 >
110 FOR 1=1 TO 10
120 LET X(I>=0
130 NEXT I
Next open a loop to generate 1000 numbers, generate the
random integers, and use the integers as subscripts to increment the
appropriate counters in the array.
140 FOR 1=1 TO 1000
150 LET V =INT< 10 $ RND<0> > +1
160 LET X<Y )=X<Y >+1
170 NEXT I
Now all that remains is to print out the contents of the array X.
180 FOR J=1 TO 10
190 PRINT J, X«C J >
200 NEXT J
210 END
Random Numbers and Simulations 245
The complete program follows:
1 00
DIM X<10>
1 10
FOR 1=1 TO
10
120
X<I)=0
130
NEXT I
140
FOR 1=1 TO
1000
150
LET Y=INT(
10*RND
160
LET X(Y)=X
< Y > +1
170
NEXT I
180
FOR J=1 TO
10
190
PRINT J,X(
j>
2 0 0
NEXT J
210
END
Run this program to see how well the random-number
generator works. Be prepared to wait about 30 seconds for the
results. If you decrease the number of integers generated, expect
the distribution of occurrence (the number of Is, 2s, 3s, etc.) to be
more skewed. If you generate more random numbers, however, the
distribution will be less skewed.
Example 4 - Random Walk
Use the graphics mode in this program to simulate a random walk
on the display screen.
The program below simulates a random walk in a city where
all the blocks are of the same size (5). Line 80 places the computer
in graphics mode. Line 140 randomly assigns the values 1, 2, 3, and
4 to the variable called WHICHWAY. Lines 150 through 520 use
WHICHWAY to determine which way to go on the next part of the
random walk.
70 REM RANDOM WALK
80 GRAPHICS 8
9 0 C 0 L 0 R 1
100 LET A=160
110 LET B=80
120 PLOT A,B
130 FOR 1 = 1 TO 500
140 LET UHIGHMAV = IN T C 4 1 RND<0)> +1
150 ON WH I CHWAY GOSUB 200 , 300 , 400 , 500
246 Hands-on BASIC
160 NEXT I
170 END
200 LET A = A-5
210 DRAWTO h,E:
220 RETURN
300 LET H=H+J
310 DRAWTO h,B
320 RETURN
400 LET B=B-5
410 DRAWTO A,B
420 RETURN
500 LET B = B + 5
510 DRAWTO A,B
520 RETURN
Example 5 - Birthday Pairs in a Crowd
What is the probability that two people in a crowd of fifty have the
same birthday? (Consider only the day of the year, not the year
of birth.) This famous problem in probability theory has surprising
results. You can attack the problem with the following strategy.
By generating random integers over the range 1 to 365, you can
simulate a birthday for each of the strangers. If you use a one¬
dimensional array for the birthdays as they are generated, it is easy to
check for identical birthdays. Beginning with the first birthday B(l),
the program checks to see if that birthday matches any remaining
birthdays. Then it does the same thing for B(2), and so on.
First look at the complete program below, then go back and
see what is taking place in each line.
100 DIM B< 50>
110 FOR 1=1 TO 50
120 LET B<I>=INTC 365*RND<0>>+1
130 NEXT I
140 LET F=0
150 FOR 1=1 TO 49
160 FOR J=I+1 TO 50
170 IF B(I)OB(J) THEN 190
180 LET F=F+1
190 NEXT J
200 NEXT I
210 PRINT "NUMBER OF BIRTHDAY PAIRS IS " j F
220 END
Random Numbers and Simulations 247
Of course, line 100 merely dimensions an array for 50 ele¬
ments. Lines 110 through 130 load the array with random integers
selected over the range 1 to 365 inclusive. In line 140, the variable
F is set equal to 0. This variable is used to keep track of the number
of birthdays to be compared with the rest of the birthdays in the
list. The value of I stops at 49 because there must be at least one
birthday left in the list against which to compare.
In line 160, the second half of the comparison is set up. J
begins at the next value past the current value of I and runs through
the rest of the list. The test for a birthday pair is made in line 170.
If no match if found, the program jumps to the next value of J. If a
match is found, the pair counter is increased by 1 in line 180. The
results are printed out in line 210. One problem with the program
is that it would record three people having the same birthday as two
birthday pairs. Can you figure out a way to fix this?
This is a very interesting program to experiment with. The
number of people in the crowd can be modified with simple changes
in the program. You can run the program many times to see how
many birthday pairs on the average will be found in a crowd of a
specified size.
11-5 PROBLEMS
1. Write a program to generate and print out 25 random numbers of
the form X.Y where X and Y are digits selected randomly from the
set 0, 1 , 2 ,3 9.
2. Write a program to generate and print out 50 integers selected at
random from the range 13 to 25.
3. What will be printed out if you run the following program?
100 FOR N=1 TO 15
110 PRINT INT<28*RND< 0 )+l>/100,
120 NEXT N
130 END
4. What will be printed out if you run the following program?
100 FOR 1=1 TO 10
110 PRINT I NT< 100$RND( 0 > >-■' 10
120 NEXT I
130 END
248 Hands-on BASIC
5. Write a program that will simulate tossing a coin, 10, 50, 500, and
1000 times. In each case, print out the total number of heads and
tails that occur.
6. Construct a dice-throwing simulation in BASIC. The dice are to be
thrown twenty times. At each toss, the program should print out
the dice faces that are uppermost.
7. Write a program to generate and print out the average of 100 random
numbers selected from the range 0 to 1.
8. Modify the program of example 5 and run it as many times as you
need to find how large a crowd must be before there is a 50 percent
chance that at least two people in the crowd have the same birthday.
9. John and Bill want to meet at the library. Each agrees to arrive
at the library sometime between 1:00 and 2:00 p.m. They further
agree that each will wait ten minutes after arriving (but not after
2:00 p.m.). If after ten minutes the other person has not arrived,
the person who is waiting will leave. Write a BASIC program
to compute the probability that John and Bill will meet. Do a
simulation of the problem using the random-number generator.
10. Suppose a basket contains colored golf balls. There are ten red balls,
five blue, two green, and eleven yellow. Write a BASIC program to
simulate drawing five balls at random from the bucket if they are
not replaced after being drawn in sequence.
11. Use the rule given in the discussion section in this chapter to generate
and print out 25 numbers selected at random from a bell curve
distribution of numbers with mean 10 and standard deviation 2.
Round off the numbers to two places past the decimal point.
12. Suppose a soap manufacturer decides to select a five-character brand
name. The first, third, and fifth characters are selected at random
from the letters BCDFGHJKLMNPQRSTVWXYZ. The second and
fourth letters are selected at random from the vowels AEIOU. Use
the rules above to write a program that generates and prints out one
hundred trial soap names.
Random Numbers and Simulations 249
11-6 PRACTICE TEST
1 . Write a BASIC program to generate and print out 100 random
integers selected from the set 1 , 2 , 3, and 4.
2. Write a BASIC program to generate and print out 100 random
numbers over the range 25 to 50.
3. What will be printed out if you run the following program?
100 FOR 1=1 TO 10
110 LET N=I NT?2*RND<0>+1)
120 IF N=1 THEN 150
130 PRINT "WHITE"
140 GOTO 160
150 PRINT "RED"
160 NEXT I
170 END
L
What will be printed out if you run the following program?
100 FOR J=1 TO 5
110 PR INT INT< 1000*RND<0> 100
120 NEXT -J
130 END
4 .
CHAPTER 12
FILES
12-1 OBJECTIVES
Files saved on diskette can be used to store and retrieve collections of
information. In this chapter you will learn to use files to manipulate
collections of information.
Storing Information to a File
You will learn to create files to store information.
Retrieving Information from a File
Once you store information, you must be able to retrieve it. You
will learn methods of retrieving information stored on files.
Modifying Information Stored on Files
It is frequently necessary to change information stored on files. You
will learn how to do this.
Working with Examples
You will learn to extract and format information stored on files.
12-2 DISCOVERY ACTIVITIES
In the past, files have been difficult to work with on computers.
Fortunately, advances in computer languages have significantly eased
the difficulties. You will find that writing programs that use files re¬
quires many techniques and concepts discussed in previous chapters.
252 Hands-on BASIC
1. You will need a formatted diskette for this activity. Turn on the disk
drive and when the busy light goes out, place the formatted diskette
in the drive and close the door. Turn on your computer and bring
up ATARI BASIC.
2. Type in the following program.
100 DIM NAMES*: 30)
110 OPEN #1,8,0, n D=GIFT.DAT"
120 PRINT "NAME: " ;
130 INPUT NAMES
140 PRINT #1,NAMES
150 PRINT "GIFT AMOUNT
160 INPUT AMT
170 PRINT #1,AMT
180 CLOSE #1
190 END
Display the program and check it, especially the punctuation.
3. Run the program. Did the disk whirr?
Enter your name and press [RETURN] . Then enter an appropriate
gift amount. Did the disk whirr again?
Did the print statements in lines 140 and 170 cause anything to be
displayed on the screen?
What happened to the information represented by NAMES and
AMT?
4. Save this program as WRITE. Recall from Chapter 4, step 20 that
you can use the SAVE command and the program name:
SAUE "D : WRITE"
Files 253
5. Type
0 0 S
then type A and press [RETURN] twice to obtain a list of files and
programs on your diskette. Is the program you saved as WRITE and
the data file named GIFT.DAT displayed on the screen?
6 .
Press B
RETURN
and type in the following program.
100 DIM NAMES' 30 >
110 OPEN #1,4,0,"0:GIFT.DAT”
120 INPUT #1,NAMES, AMT
130 CLOSE #1
140 END
Display the program and check it. Run the program. Did the disk
whirr?
Was a question mark placed on the screen by line 120?
Was anything displayed on the screen by the program?
7. Add line 125 as follows
125 PRINT NAMES, AMT
Run the program. The information is read from the file in line 120.
Is that enough to make the information useful?
8 .
Save this program as READ (See step 4.)
254 Hands-on BASIC
9. You must open and close a file each time you used it. To write to
a file, use a PRINT statement. To read from a file, use an INPUT
statement.
10. Now let's move on to using files with more than one record. Load
the program WRITE. Display the program. Add the following lines.
115 PRINT "TYPE QUIT FOR NAME WHEN DONE"
135 IF NAME$= 11 QUIT" THEN 180
175 GOTO 128
Display the program once again to check its accuracy. Run the
program. At the input prompt, enter several names and amounts
as you choose. Enter at least three records and amounts above and
below 50. (Note: The disk will whirr after four names and amounts
have been entered even if you are not finished.) What do you type
to end the information entry?
Try it and see if you were correct.
11. Save this new program with the same name: WRITE.
12. Load READ. Display the program. Add the following line.
128 G0TO 12O
What do you think will happen if you run the program?
Run the program and see if you were right.
13. The ERROR 136 error message signifies end of file and can be
avoided by adding the following line.
122 TRAP 130
Run the program. Did the error message occur this time?
Files 255
14. Now extract some information from your file. Display the program.
Add the following line.
121 IF AMT<50 THEN 128
Run the program. Were all the names printed out?
15. You can also compile information from the file. Display the pro¬
gram. Change lines 121 and 140 and add lines 90 and 150 as
follows:
121 IF AMT>50 THEN C = C+1
140 PRINT "THERE ARE ”” GIFTS OUER 50"
90 LET C=0
150 END
Now delete line 125. Run the program. Does the number displayed
agree with the information you wrote out to file?
You may wish to display the program and study it.
16. Now let’s add some things up. Load READ once again. Display the
program. Add the following lines.
90 LET SUM = 0
123 LET SUM=SUM+AMT
135 PRINT "TOTAL GIFT SUM IS " ; SUM
Delete lines 125 and 140. Display the program. Run the program.
What was the total of the gifts in the information you entered?
256 Hands-on BASIC
17. That ends the discovery exercises. Turn off the computer and go on
to the discussion.
12-3 DISCUSSION
Several BASIC statements can be used with files. The ones you have
learned are flexible enough to cover almost every use of files. As you
saw in the discovery exercises, the OPEN statement prepares a file
so that information can be written to or read from it. The PRINT
statement causes information to be written to a file that has been
opened for output. The INPUT statement allows information to be
read from a file opened for input. All files that are opened must be
closed before you run a program or before you change the status of
the file. For instance, you must use the CLOSE statement to change
file status from open to accept information to open to be read.
Storing Information to a File
To access a file, you must use the OPEN statement. For example,
110 OPEN #1,8,0, u DFILEONE n
prepares FILEONE to have information written to it. The statement
will create the file, if necessary.
The #1 in line 110 is called an input/output control block
(IOCB). For the purposes of this book, you need to know only that
an IOCB is necessary in every OPEN statement and that you can
freely use IOCB's #1 through #5.
The second number in the OPEN statement, 8 in the example
above, determines the operation to be performed with the file. The
number 4 indicates an input operation and prepares the file to have
information read from it. The number 8 indicates an ouput opera¬
tion and prepares the file to have information written to it. The
number 9 also signifies an output operation but prepares the file to
have information added to it.
In this book, the third number is always 0. The only other
value allowed, 83, causes the printer (if one is attached) to print
sideways.
The last portion of the OPEN statement indicates which file
is to be used.
Once a file is opened for output, you can write to the file. To
write to a file, a PRINT statement is required. For example.
Files 257
lie OPEN #1,8,0, "'0 = FILEONE"
120 PRINT #1}NAMES
will set up FILEONE to accept data from subsequent PRINT state¬
ment. When you write to a file, the PRINT statements you use must
have an IOCB. The data contained in NAMES will be written to a
record in the file. The information items will be written out to the
file in the order that they appear in the program.
In the following example, a file is opened and some informa¬
tion is written to it.
100 DIM NAME$< 25 >, GRADESC 1 >
110 OPEN #1,8,0,"D : QUIZ.DAT"
120 PRINT "NAME; "
130 INPUT NAMES
140 IF NAMES = "QUIT 11 THEN END
150 PRINT #1;NAMES
160 PRINT 11 LETTER GRADE : "
170 INPUT GRADES
180 PRINT #1;GRADES
1 9 0 G0TO 120
In line 110 the file QUIZ.DAT is opened (created if necessary).
Lines 150 and 180 write the information, in this case the student's
name and grade, to the file QUIZ.DAT. The .DAT appended to the
file name QUIZ is an extension allowed in file names. You can
extend the file name with one to three letters following a period.
This addition to the name can be very helpful when you display the
file directory; for instance the extension DAT to the right of the file
name helps you see at a glance which files contain data.
Also note that there is no CLOSE statement in this example.
The END statement closes all files that are open. However, files are
often opened and closed several times in a program. The CLOSE
statement is necessary because the END statement does not close
files until the program stops running.
When you use the number 8 to open a file for output, any
information in that file is lost. Therefore, use number 8 only when
you don't need the information in the file or when the file is empty.
However, if you wish to add information to a file, then use a state¬
ment such as
150 OPEN #1,3,0,"D=FILEONE
258 Hands-on BASIC
This statement prepares FILEONE for output, and all information
written to the file will be added to the end of information that is
already on it. You cannot use this option unless FILEONE already
exists.
Retrieving Information from a File
To read information from a file, you must use an OPEN statement
and INPUT statements, as in the following example.
100
DIM NAMES': 25 >, GRADES-: 1 )
110
OPEN
#1,4,0, "D = QUIZ.DAT"
120
TRAP
160
130
INPUT
#1 } NAMES, GRADES
140
PRINT
NAMES, GRADES
150
G U T 0
120
160
END
Recall
that without line 140, nothing will be displayed on the
screen. The INPUT statement in line 130 only reads information
into the variables. What you instruct the program to do with the
variables depends on the outcome you desire.
The TRAP statement in line 120 traps the end-of-file error
that will occur in line 130. Instead of displaying the error message,
and stopping the program, the computer will branch to line 160.
Other types of errors can be treated in this way as well because the
TRAP statement takes control of the program when an INPUT error
occurs and directs execution to a specified line number.
You have been using sequential files throughout this chapter.
Sequential files are files on which records (information) are placed
one after another. When reading from a sequential file, you must
start at the beginning of the file and read each record until you reach
the one you wish to process. Another kind of file called a random
access file is also available on your ATARI computer. Random access
files allow you to read from and write to any record by indicating
which record you want to use. They are, however, more difficult
to learn than are sequential files. Sufficient versitality of sequential
files will be seen in the examples given below. Certain tasks are
better handled with sequential files than with random access files.
Information about random access files can be found in your Disk
Operating System II Reference Manual .
Files 259
12-4 PROGRAM EXAMPLES
The following set of programs can be used to create and maintain a
mailing list for advertising and billing purposes.
Example 1 - Mail List Data Entiy Program
A mailing list contains names, addresses, and other information
about individuals. Thus, the program might request the following
items.
FIR 3 T N A M E : (You type in)
LAST NAME : (You type in)
STREET : (You type in)
CITY : (You type in)
ZIP C 0 D E : (You type in)
BALANCE : (You type in)
You would request this information about every person to
be placed on the mailing list. Termination of input could be ac¬
complished by entering QUIT for the first name. The information
would then be stored to a file called MAIL.DAT.
The complete program follows.
80 REM MAIL LIST DATA ENTRY
90 REM REPLY WITH N TO CREATE A NEW FILE
100 DIM FIRST$< 18 >, LAST$< 15 >
110 DI M STREETS^ 25 >, CI TY$< 15 >, ANS$< 3 >
120 PRINT "DO YOU WISH TO ADD DATA"
130 PRINT "TO THE CURRENT FILE? CY.-TD ";
140 INPUT ANSS
150 IF ANS$ ="Y" THEN 180
160 OPEN #1,8,0,"D=MAIL.DAT"
170 GOTO 190
180 OPEN #1,9,0,"D : MAIL.DAT"
190 PRINT "USE QUIT FOR FIRST NAME TO END
200 PRINT "FIRST NAME = "
210 INPUT FIRSTS
220 IF FIRST$="QUIT" THEN 400
230 PRINT #1 i FIRSTS
240 PRINT "LAST NAME = ";
250 INPUT LASTS
260 Hands-on BASIC
260
PRINT
#1.: LASTS
270
PRINT
"STREET-
2 8 0
INPUT
STREETS
280
PRINT
#1.: STREETS
300
PRINT
"CITY--
310
INPUT
CITYS
320
PRINT
# 1 .: CI T YS
330
PRINT
"ZIP CODE’- ".:
340
INPUT
ZIP
350
PRINT
#1; ZIP
360
PRINT
"PAYMENT BALANC
370
INPUT
BAL
3 8 0
PRINT
# 1 , B A L
3 9 0
GOTO
190
400
CLOSE
#1
4 1 0
END
Save this program under the name DATAENTR. You will be
using it again.
Example 2 - Mailing Label Program
This program will use the MAIL.DAT file to create mailing labels
The labels should have three lines as shown below.
GEORGE JONES
1234 DATAFILE DRIUE
SAN JOSE.. CA 95009
The complete program follows.
90 REM MAILING LABEL PROGRAM
100 DIM FIRST$< 10 >, LASTS': 15 >
110 DIM STREETS*; 25 >, C I TV$< 15 >
120 OPEN #1,4,0,"D = MAIL.DAT"
130 TRAP 230
140 INPUT #1 ; FIRSTS, LASTS
150 INPUT #1;STREETS, Cl TVS
160 INPUT #1 j ZIP,BAL
170 PRINT FIRSTS.:" LASTS
180 PRINT STREETS
1 90 PR I NT CI TVS.: " , CA " ZI PS
Files 261
200 PRINT
210 PRINT
220 G0TO 140
230 END
Save this program under the name LABELS.
Example 3 - Selected Labels Program
It is fairly easy to modify the previous program to select records
in a file based on a condition. In this example, the program
generates labels for bills by selecting those customers with outstand¬
ing balances. You modify the program in example 2 simply by
changing line 90 and adding line 165 so that the complete program
reads as follows.
90 I
REM SELECTED L
ABELS
: PROGRAM
1 0 0
DIM F
I RST$( 10
>, LAS
TSC 1 5 >
1 10
DIM S
TREETS, C
I TVS
120
OPEN
#1,4,0,"
D * MAI
!L.DAT"
130
TRAP
2 3 0
140
INPUT
# 1 , F IR S
TS, LA
STS
150
INPUT
#1 ; STREETS, C
I TVS
160
INPUT
#1.;ZIP,
BAL
165
IF Bh
L=0 THEN
140
170
PRINT
FIRSTS;
i! 11 ; |_
A STS
180
PRINT
STREETS
190
PRINT
Cl TVS; "
, Ch
" ; 21 PS
2 0 0
PRINT
210
PRINT
220
G 0 T 0
140
230
END
Save this program under the name LABSEL.
Example 4 - Modifying the MAIL.DAT file
This program will allow you to modify any of the items in a record
in the MAIL.DAT file. In order to do this, the program must know
which record and item you wish to change. The program should
ask for a last name and then display all the items for a record where
the LASTS matches the last name you enter, then it should ask you
262 Hands-on BASIC
to modify one or more items in the record if the record you wish to
modify is being displayed. If not, the program should continue to
display the other records you wish to modify.
The complete program follows.
90 REM MODIFY h RECORD IN THE MAIL LIST
100 DIM FIRSTSC 18 >, LASTSC 15 >
110 DIM STREET$< 25 >, CITYSC 15 >, ANSSC 3 >
120 OPEN #1,4,0,"D'MAIL.DAT"
130 OPEN #2,8,0,"D = TEMP.DAT"
140 PRINT "PLEASE ENTER THE LAST"
150 PRINT "NAME OF THE RECORD"
160
170
180
190
2 0 0
210
220
230
240
250
260
270
280
290
3 0 0
310
320
330
340
3 5 0
360
370
3 8 0
PRINT "YOU WISH TO MODIFY"
INFUT NAMES
INPUT #1 FIRSTS, LASTS, STREETS
INPUT # 1 CI TVS, ZIP, BAL
IF NAMES=LAST$THEN 230
GOSUB 820
G 0 T 0 1 8 0
PRINT "1
PRINT "2
PRINT "3
PRINT "4
PRINT "5
PRINT "6
PRINT "7
")FIRSTS
"jLASTS
" STREETS
" .; CITYS
" Z IF'
" ; BAL
EXIT "
PRINT "ENTER THE NUMBER OF THE"
PRINT "ITEM YOU WISH TO MODIFY "
INPUT N
IF N=7 THEN 350
0 N N G 0 S U B 7 0 0,7 2 0,740,76 0,7 8 0,8 0 0
PRINT "DO YOU WISH TO MODIFY ANOTHER"
PRINT "ENTRY IN THIS RECORD? < Y/N > "
INPUT ANSS
IF ANS$="Y" THEN 230
TRAP 530
390 PRINT #2- FIRSTS ' PRINT #2.; LASTS
400 PRINT #2.; STREETS'PRINT #2.; Cl TYS
410 PRINT #2;ZIP'PRINT #2.; BAL
420 PRINT "MODIFY ANOTHER RECORD? "
430 INPUT ANSS
440 IF ANS$="Y" THEN 140
450 TRAP 530
Files 263
460 INPUT #1.; FIRSTS^ PR I NT #2; FIRSTS
470 INPUT #1; LASTS= PRINT #2.; LASTS
480 INPUT #1 STREETS = PRINT #2; STREETS
490 INPUT #1;CITYS : PRINT #2 = Cl TVS
500 INPUT #1 ■, ZIP = PRINT #2; ZIP
510 INPUT #1;BAL= PRINT #2;BAL
520 GOTO 460
530 CL 0SE #1 : C L 0SE #2
540 OPEN #1,8,O,"D = MAIL.DAT"
550 OPEN #2,4,O,"D = TEMP.DAT"
560 TRAP 64 0
570 INPUT #2;FIRSTS^PRINT #1;FIRSTS
580 I NF'IJT $2LASTS : PR I NT #1 } LASTS
590 INPUT #2;STREETS:PRINT #1}STREETS
600 INPUT #2;CITYS:PRINT #1;CITYS
610 INPUT #2;ZIP = PRINT #1;ZIP
620 INPUT #2; BAL : PR I NT # 1j BAL
630 G0TO 560
640 END
700 PRINT "FIRST NAME :
705 INPUT FIRSTS
710 RETURN
720 PRINT "LAST NAME = "
725 INPUT LASTS
730 RETURN
740 PRINT "STREET: ■■ }
745 INPUT STREETS
750 RETURN
760 PRINT "CITY: "
765 INPUT CITYS
770 RETURN
780 PRINT "ZIP CODE:
785
INPUT
ZIP
790
RETURN
8 0 0
PRINT
"BALANCE:
805
INPUT
BAL
8 1 0
RETURN
8 2 0
PRINT
#2 } F IRSTS : PR I NT #2; LASTS
8 3 0
PRINT
#2STREETS = PRI NT #2 i CITYS
8 4 0
PRINT
#2;ZIP:PRINT #2;BAL
850 RETURN
Save this program under the name MODIFY.
264 Hands-on BASIC
Example 5 - Menu-Driven Mailing Program
This program will give you a menu to select any of the previous
activities. It will allow you to use this set of programs to maintain
a mailing list for use in billing individuals. This is a very effective
way to incorporate several program modules into one short program
that will accomplish a desired task.
The program should begin by printing the possible activities
that you can select. The program might print
1. ADD A NEW RECORD
2. COMPLETE SET OF LABELS
3. SELECTED SET OF LABELS
4. MODIFY A RECORD
5. EXIT THE PROGRAM
The complete program follows.
1 0 0
PRINT
"1. ADD A NEW RECORD
ll
110
PRINT
" 2 . COMPLETE SET OF
LABELS"
120
PRINT
"3. SELECTED SET OF
LABELS"
130
PRINT
"4. MODIFY A RECORD"
140
PRINT
"5. EXIT THE PROGRAM
H
150
PRINT
"CHOOSE A NUMBER "
160
INPUT
N
170
IF H
=
5 THEN END
180
ON N
G
0 T 0 3 O 0 .. 4 0 0 .■ 5 0 0.. 6 0 0
3 0 0
RUN "
0
:DATAENTR"
4 0 0
RUN "
D
: LABELS"
5 0 0
RUN "
D
=LABSEL"
6 0 0
RUN "
D
:MODIFY"
Save this program under the name MENU.
If you want the program to return to the main menu-driven
program above after it has called for the execution of another
program, modify the END statement in each of the programs
DATAENTR, LABELS, LABSEL, and MODIFY. For instance, you
would add the following two lines
418 RUN "D : MENU
420 END
Files 265
to DATAENTR program. These same lines, but with different line
numbers, should replace the END statements in the remaining pro¬
grams.
12 — 5 PROBLEMS
1. Design an appropriate record structure for a file that will be used to
index your cassette tape collection. Determine valid ATARI BASIC
variable names for each item in the record structure.
2. Design an appropriate record structure for a file that will be used to
keep track of your checkbook entries.
3. Design an appropriate record structure for a file that will be used to
inventory your household possessions.
4. Write out an appropriate record structure for a file that will be used
to keep your personal mailing list. Remember that birthdays and
anniversaries are important to your friends.
5. Write a program that will use a file called CHARGE to manage your
charge cards. Each record should have the following structure.
Variable
Description
Approximate Length
CARDS
Name of Card
20
NAMES
Name of Store
30
DATES
Date of Purchase
10
DESS
Description of Purchase
50
AMT
Amount of Purchase
8
The program should allow you to total the amount of money you
have charged to each card in the entire file.
6. Write a program that uses the record structure from problem 4 to
manage your personal mailing list. The program should allow you
to print out labels for your Christmas cards and for messages to
your friends at work.
266 Hands-on BASIC
12-6 PRACTICE TEST
1. If you run the following program:
100 DIM NAMES< 20), MESSAGES'50 >
110 OPEN #2,8,0, H D = FILETH0 11
120 INPUT NAMES
130 PRINT #2.i NAMES
140 INPUT MESSAGES
150 PRINT $2 .= MESSAGES
160 CLOSE #2
178 END
a. What file will be used?
! ___
b. How many characters are allowed in each variable name?
L
c. How many items are placed in the file?
2. Write a program line that opens a file named TRIAL.DAT. The line
should allow information to be written to the file.
L
3. Write a program that will read and print the three information items
from variables AS, B$, and C$. Each variable has a length of 10.
The variables are in a file named TEST1.DAT. Be sure to close the
file.
Files 267
4. What is wrong with the following program line?
200 OPEN #1,4,0,"D,FI LEONE"
i_
5. Will the following program line allow information to be added to
the file FILEONE?
200 OPEN #2,9,0, H D=FILEONE"
APPENDIX A
GLOSSARY
ABS|X) A BASIC function that takes the absolute value of X.
Positive values of X remain positive. Negative values of X
become positive.
Arithmetic Operators Addition +, subtraction , multiplication *,
division /, and exponentiation X
ASC(A$) A BASIC function that converts the first character in A$
to its equivalent position number in the ASCII character set.
BASIC An acronym for "Beginners All-Purpose Instruction Code".
More people know how to program computers in BASIC than
any other language.
CHR$(M) A BASIC function that returns the Nth character from
the ASCII character set.
CLOSE A file statement that terminates access to a text file on the
diskette in the disk drive.
COLOR A statement that chooses the color register to be used in
color graphics.
Control Characters These are chara cter s typed on the keyboard
while holding down the |CTRL| or [CONTROL] key. They are
used to send special signals to the computer.
Cursor A square displayed on the TV screen that shows where the
next typed character will be displayed.
DATA A statement used to hold information within a program.
This information is called for with the READ statement.
Deleting BASIC Statements Type t he line nu mber of the statement
to be deleted and then press
RETURN
270 Hands-on BASIC
DIM A statement used to specify the size and reserve space for
arrays.
Double Subscripts Indicated within parentheses following a variable
name, and separated by a comma. Used to specify a row
and column number in an array. A(3,5), for example, means
the element in the two dimensional array A at row 3 and
column 5.
DOS Diskette A diskette that has been formatted using the DOS
disk operating system. These diskettes can be used to store
programs and files.
DRAWTO A statement that draws a line from the current position
of the grtaphics pen to the point specified.
Editing Making corrections or changes in a program or data.
END Marks the end of a BASIC program or the end of the main
program.
E Notation A notation used in BASIC to express either very large
or very small numbers.
FILE A collection of information that is created and used by the
ATARI BASIC file statements.
FOR NEXT Statements used in BASIC to set up loops.
GET A statement that calls for information from the keyboard
without placing a question mark on the screen.
GOSUB A statement used to transfer program control to a sub¬
routine.
GOTO An unconditional branch statement.
INPUT A statement that calls for input of information from the
keyboard.
Inserting BASIC Statements Type in the statement using a line num¬
ber not already in use.
IF THEN A conditional branch statement.
INTfXJ A BASIC function that takes the integer part of X. The
integer part of X is defined as the first integer less than or
equal to X.
LEN(A$) A BASIC function used to determine the length of a string
in characters. For example, if AS = “DOG" then LEN(A$)
is 3.
Glossary 271
LET Identifies an assignment statement. It is always followed by a
variable name, an equal sign, and a BASIC expression. The
LET in the assignment statement is optional.
LIST A command used to display the program in memory.
LOAD A command that loads a file from a diskette to the memory.
MEW A command that erases the current program in memory.
Mumeric Variable Mames ATARI BASIC allows variable names up
to 110 characters long. The first character must be a letter.
OM M GOSUB A statement that branches to one of several sub¬
routines depending upon the value of N.
OM M GOTO A statement that branches to one of several numbered
lines depending upon the value of N.
OPEM A file statement that opens the specified file for input or
output operations.
PLOT A statement that plots a point at the position specified
PRIMT A statement that sends information from the computer to
the screen.
Random Mumbers A sequence of numbers generated by the RND
function. They appear to have no pattern or relationship to
one another.
READ A statement that calls for input of information stored in
DATA statements within the program.
RECORD A record is a collection of information stored in a text
file created and used by the ATARI BASIC file statements.
Replacing BASIC Statements Retype the statement to be replaced
including the line number.
RETURM A statement used to transfer program control back from
a subroutine to the main program.
RMD A BASIC function used to generate random numbers.
RUM A command used to tell the computer to begin execution of
the program in memory.
SAVE A command that saves a program from memory to diskette.
For example, SAVE “DrAVERAGE" would save the program
currently in memory to the diskette in the disk drive under
the name AVERAGE.
272 Hands-on BASIC
SETCOLOR Stores the hue and luminance color data in a particular
color register.
SGN(X) A BASIC function that determines the sign of X. SGN(X)
is +1, 0, —1 as X is positive, zero, or negative respectively.
Single Subscripts Indicated within parentheses following a variable
name. Used to specify a particular element in an array. A(6),
for example, means the sixth element of the one dimensional
array A.
SOUND Controls the register, sound pitch, distortion, and volume
of a tone or note.
SQR(X) A BASIC function that takes the square root of X. X cannot
be negative.
String Variable Names BASIC string variable names are allowed to
be up to 110 characters long. They must start with a letter
and end with a $ sign.
System Master Diskette A DOS diskette that contains a number of
useful programs.
APPENDIX B
PRACTICE TEST SOLUTIONS
Chapter 1
1. Press the |RETUR/\Z[ key.
2. Press the |RESETl or [SYSTEM RESET! key.
3. *
4. Press the [CLEAR ] key.
5. Division.
6. The number 2 will be displayed on the screen.
7. The string 25/5+2 will be displayed on the screen.
8. Move the cursor to the G in PRING with the CTRL
or
CONTROL
key and the left arrow key (<—). Then type in a T and press
Chapter 2
1. Press the [RETURN] key.
2. Press the BREAK key.
3. Press BREAK
274 Hands-on BASIC
4. The statement PRINT C has no line number.
5. The number 2 would be displayed on the screen.
6. Up to 110 characters.
7. Type the line using a line number not already in the program.
8. Retype the line including the line number.
9. Type the line number and press [RETURN
10. Type LIST and press [RETURN
11. Press the [CLEAR] key.
12. Type RUN and press [RETURN
13. Type NEW and press [RETURN]
14. A character string variable always ends with a $.
Chapter 3
1. A square with its center at the center of the screen.
2. A house with the peak of the roof at the center of the screen.
GRAPHIC
S 8
■ Dl HT i
•«!_*_*! -L
60 f
C; L-1
DRAWTO
2 8 0 j
. 80:DRA
j u t f j
2 y
0 ,
20
DRAWTO
2 2 Ei j
, 2 0 : D R A
i WTO
22
0
8 0
a. PLOT
160,
80 b.
P |_ n
T 0
, 0
c.
PLOT
d. PLOT
2 4 0 ■
1 5£i
a. By typing LF
: A P H I C S
!=!
b.
CO
LOR
1
6. Moves a line segment down the middle of the screen
Practice Test Solutions 275
Chapter 4
1. a. * b. ^ c. /
2. a. Exponentiation b. Multiplication and division c. Addition
and subtraction
3. Left to right.
4. 100 LET A = ( 4 + 3$B-*'D > A 2
5. 4
6. a. 5.16E+06 b. 3.14E 05
7. a. 7258000 b. 0.001437
/ then
a.
b.
c.
d.
e.
f.
g*
Type
Type
Type
Type
Type
Type
Type
R ETURN
RE TURN
LOAD "D : (name of program) 1 ' and press
SAUE “D : (name of program)" and press
DOS, THEN D and follow directions.
NEW and press [R ETURN .
LIST and press RETURN .
RUN "D : (name of program)" and press /RETURN.
DOS, then A and press [RETURN] twice.
10. Use the left arrow key to mov e the cur sor to the err or an d type
the correct character and press
RETURN] . Recall the |CTRL | key is
required with the left arrow.
1 .
Chapter 5
i ;
etc.
10
4
1 1
12
2. a. By assignment (e.g., 100 LET A = 3 ) b. INPUT statements
c. READ and DATA statements
276 Hands-on BASIC
3. A string.
4. To provide information within the program for the benefit of the
programmer or user.
5. DATA.
6. Y = 3 will be printed out.
7. Four
8. As many as needed.
9. 1 3
13
10. 22
READY
11. ID0 PRINT ,! INPUI N0 . QF MILES
110 INPUT N
120 LET K=1.609*N
130 PRINT N.;" MILES EQUALS "
140 P RINT KJ “ KIL 0 METE R S"
150 END
Chapter 6
1 . 6
10
14
18
BETTER
BEST
L U U D
BETTER
BEST
ERROR 6
AT LINE 100
Practice Test Solutions 277
3.
4.
5.
100 PRINT "HOW MANY WIDGETS".;
110 INPUT N
120 IF N< = 20 THEN 160
130 IF N< =50 THEN 180
140 LET U =1.5
150 GOTO 190
160 LET 1J = 2
170 GOTO 190
180 LET U=1.8
198 LET P -N t U
200 PRINT "PRICE PER WIDGET IS "U
210 PRINT "TOTAL COST OF ORDER IS "P
220 PRINT
230 GOTO 100
240 END
100 LET X=0
110 PRINT X,X + 5,X+10
120 LET X = X +15
130 IF X<=175 THEN 110
140 END
100 PRINT "WHAT WAS THE SPEED LIMIT? "
110 INPUT A
120 PRINT "SPEED ARRESTED AT?
130 INPUT B
140 LET X = B-A
150 IF X>40 THEN F=80
160 IF X<=40 THEN F = 40
170 IF X< =30 THEN F=20
180 IF X<=20 THEN F=10
190 IF X<=10 THEN F=5
200 PRINT "FINE IS " F" DOLLARS"
210 END
Chapter 7
16
14
f.
278 Hands-on BASIC
2 . 1
9 4 8 12
3. a. 6 b. 7 c. 22.8 d. -1
4. The loops are crossed.
5. 100 PR I NT " MILES", " KILOMETERS "
110 PRINT "--"
120 FOR M=10 TO 100 STEP 5
130 PRINT M,1.609*M
140 NEXT M
150 END
1 0 0
DATA
10
1 10
DATA
25,21
120
READ
N
130
LET S
= 0
140
FOR I
= 1 TO
150
READ
y
160
LET S
=s+x
170
NEXT
I
180
PRINT
S / N
190
END
7. a. A triangle b. 28 c. across
Chapter 8
1. To save space for an array.
2. X(3,4)
3.
1 0 0
DIM AC
50 >
110
PRINT
"HOW MANY NUMBERS "
120
INPUT
N
130
PRINT
"WHAT ARE THE NUMBER
140
FOR 1 =
1 TO N
150
INPUT
y
160
LET AC
I >=x
170
NEXT I
Practice Test Solutions 279
180 LET 8=0
190 FOR 1=1 TO N
200 IF H'::i><=0 THEN 220
210 LET S=S+A<I )
220 NEXT I
230 PRINT "SUM OF POSIT IUE ELEMENTS IS "
240 END
90
DIM X< 46 >
1 0 0
FOR R=1 TO
4
110
FOR C=1 TO
6
120
LET X( R .. C >
= 4
130
NEXT C
140
NEXT R
150
END
2 0
0 2
0 0 0
0 0 0
0 0
2 0 0
0 0
0 2 0
0 0 0 0 2
6. a. 1 00 DIM At 2,3 > b. A(2,3) = 4 c. A(X,Y) = A(l,2) = 3
d. A(A(1,1)/ A(2,2)) = A(l,2) = 3
Chapter 9
1. By appending $ to a numeric variable name.
2. False
3. A$< 5 .■ 1 3 >
4. 90 DIM A$<50>
100 INPUT A$
110 FOR X=LEN< A$ > TO 1 STEP -1
120 PRINT A$( 1 .. X >
130 NEXT X
140 END
280 Hands-on BASIC
AB
ABC
ABCD
ABODE
etc.
A B C D E F G HIJ K L M N 0 P Q R S T U U M X Y Z
Chapter 10
1. The second note.
2. Type in GOSUB (line number at beginning of subroutine.)
3. RETURN
4. WHITE
RED
BLUE
1 .
2.
Chapter 11
100 FOR 1 = 1 T 0 10 0
110 LET X =IN T<4 $ R N D<0> +1 )
120 PRINT X,
130 NEXT I
140 END
100 FOR 1 = 1 T 0 10 0
110 LET X=25+25$RND<O >
120 PRINT X,
130 NEXT I
140 END
Practice Test Solutions 281
3. The output will be randomly selected from WHITE and RED. Three
program outputs are shown to indicate the random nature of the
process.
< 1 >
( 2 )
( 3 )
RED
WHITE
WHITE
RED
WHITE
RED
WHITE
RED
WHITE
WHITE
WHITE
WHITE
RED
WHITE
WHITE
RED
RED
WHITE
RED
RED
RED
WHITE
RED
WHITE
RED
WHITE
WHITE
RED
WHITE
RED
4. Five random numbers of the form X.XX over the range 0.00 to 9.99.
Three program outputs are shown below to illustrate the random
nature of the process.
l'
1 >
r
2 )
f
3 ?
0
51
6
S3
1
15
9
34
4
04
y
87
9
0 8
9
06
9
26
9
26
f,
71
2
59
cr
98
o
15
"7
05
Chapter 12
1. a. FI LET WO b. 20 and 50 c. 2
2. 110 OPEN # 1,8,0, " 0 = TR I AL . DAT "
100 D IM A$< 1 0 ) B$< 10 >, C$< 10 >
110 OPEN #1,4,0,»D:TEST1.DAT"
120 INPUT #1 ; A$, B$, C$
130 PRINT AS, B$, C$
1 4 0 G 0 T 0 1 2 0
150 END
3.
282 Hands-on BASIC
Good programming practice would call for the statement TRAP 150
just before line 120 to avoid an error message and to close the file
smoothly.
4. The correct program line is
288 OPEN #1,4,8,"D : FI LEONE"
5. Yes, the second number, 9, is exactly the value needed to add to a
file.
APPENDIX C
SOLUTIONS TO
ODD-NUMBERED
PROBLEMS
Chapter 5
1 .
1 0 0
REM CHhP 5
, PR OB
110
READ A,B,C
, D
120
DATA 10,9..
1 , 2
130
LET S=A+B
140
LET P=C*D
150
PRINT S,P
160
END
3.
1 0 0
REM CHAP 5
, PR OB
110
READ A,E:,C
, D
120
DATA 21,18
6.« 3
130
PRINT A
140
PRINT B
150
PRINT C
160
PRINT D
1 70
END
5.
There
is no value assigned to C
7.
1 0 0
REM CHAP 5
, PROB
110
PRINT "CAS
H =
120
INPUT C
284 Hands-on BASIC
130 PRINT "MARKETABLE SECURITIES = ".;
140 INPUT M
158 PRINT "RECEI CABLES = ".;
160 INPUT R
170 PRINT "LIABILITIES = ";
180 INPUT L
190 LET A = < C + M + R X- L
200 PRINT "ACID-TEST RATIO = ";A
210 END
9. The program loops back to line 100 where A is set equal to 1 after
each printout. The program can be corrected by changing line 130
as follows.
130 G0TO 110
11. The problem lies in statements 100, 110, and 120. The values
of L, W, and H are supposed to be printed out, but they haven’t
been defined. The computer will assign the value zero to the three
variables and these zeros are printed out by lines 100, 110, 120.
The program may be corrected by deleting line 130 and L, W, and
H at the ends of lines 100, 110, and 120. Now, the following lines
need to be added.
105 INPUT L
115 INPUT U
125 INPUT H
13. 100 REM CHAP 5, PR0B 13
110 DATA 21423,21493,5
120 DATA 5270,5504,13
130 DATA 65214,65559,11.5
140 READ R1,R2,G
150 LET M=< R2-R1 >,- G
160 PRINT M
170 GOTO 140
180 END
15. 100 REM CHAP 5, PROB 15
110 DATA 92,63,75,82,72,53,100,89,70,81
120 READ A,B,C,D,E,F,G,H,I,J
130 PRINT <A+B+C+D+E+F+G+H+I+JV10
140 END
Solutions to Odd-Numbered Problems
100 REM CHAP 5, FEQB 17
110 PRINT "QUOTED INTEREST RATE < PERCENT
120 INPUT R
130 PR I NT"NUMBER OF TIMES COMPOUNDED PER
140 INPUT M
1 50 LET T=( < 1 +R1 004M > A M- 1 )T 1 00
160 PRINT "TRUE ANNUAL INTEREST RATE IS"
170 PRINT T
1S0 END
100 REM CHAP 5, PROB 19
1 1 0 PR I NT "INITIAL I NUESTMENT "
120 INPUT P
130 PRINT "ANNUAL INTEREST R A T E < 'O "
140 INPUT I
150 PRINT "YEARS LEFT TO ACCRUE INTEREST
160 INPUT N
170 LET T=P*< 1 + I 1 00 y-N
180 PRINT "TOTAL UALIJE IS ";T
190 END
Chapter 6
100 REM CHAP 6, PROB 1
110 INPUT XjY
120 IF X>Y THEN 150
130 PRINT Y
140 GOTO 160
150 PRINT K
160 END
100 REM CHAP 6, PROB 3
110 LET S=0
120 LET K=1
130 LET S=S+K
140 LET X=X+1
150 IF X<=100 THEN 130
160 PRINT S
170 END
ERROR-
6 AT LINE 120
286 Hands-on BASIC
7. 100 REM CHAP 6, PROP 7
110 LET S=0
120 READ X
130 IF v = 9999 THEN 180
140 IF X\ 10 THEN 120
150 IF X>10 THEN 120
160 LET 8 = S+X
1 7 0 G 0 T 0 1 2 0
180 PRINT S
190 DATA -1.. 22.■ l?.• S, 4.. ?.- 9999
280 END
9. 10 0 R E M C H A P 6 .■ P R 0 B 9
110 LET C=1
120 LET T=0
130 LET N=1
140 LET T=T+W
150 LET C=C+1
160 LET W=2*W
170 IF C< =22 THEN 140
180 PRINT T•••' 1 00
190 END
11. The number 83 will be printed out. The program finds the largest
number contained in the two DATA statements.
13. 100 REM UHAP 6 .> PROB 13
110 PRINT "LIST PRICE <$> ".;
120 INPUT L
130 PRINT "DISCOUNT RATE ";
140 INPUT R
150 LET D=L*<l-R/100)
160 PRINT "DISCOUNTED PRICE IS"
170 PRINT D.; " DOLLARS"
180 END
15. 100 REM CHAP 6, PROB 15
110 INPUT A,B
120 IF A>=10 THEN 130
121 GOTO 150
130 IF B> = 10 THEN 140
131 GOT 0 15 0
140 PRINT A+B
Solutions to Odd-Numbered Problems 287
17.
141 GOTO 210
150 IF A<10 THEN 160
151 GOTO 180
160 IF B<10 THEN 170
161 GOTO 180
170 PRINT A*B
171 GOTO 210
180 IF A<B THEN 200
190 PRINT A-B
191 GOTO 210
200 PRINT B-A
210 END
100 REM CHAP 6, F'ROB 17
110 PRINT "GROWTH RATE (.’4) "
120 INPUT R
130 LET N = 0
140 LET Q=1
150 LET Q = Q*C 1+R--100 >
160 LET N=N+1
170 IF Q< = 2 THEN 150
180 PRINT "NUMBER OF GROWTH PERIODS
IS " :< N
190 END
TO
8 9
REM
CHAP 6, PROB 19
90
D IM
Y$< 1 >
i 0 0
OPEN #1,12,0, "K = "
1 10
GRAPHICS 8
120
LET
A= 160
130
LET
B = 96
140
COLOR 1
150
PLOT A,B
160
D R A W T 0 A , B
1 70
GET
#1,K
180
LET
Y$=CHR$< x :■
190
IF
Y$="D" THEN B=B+10
200
IF
Y$="U" THEN B=B-10
210
IF
Y$= " L " THEN A = A -1 0
220
IF
Y$="R" THEN A = A +10
230
IF
Y$="Q" THEN 250
DOUBLE
288 Hands-on BASIC
240 LOTQ 160
250 END
Chapter 7
100 REM CHRP 7.. PROB 1
110 PRINT "N","SQR<N )"
120 PRINT
130 FOR N = 2 TO 4 STEP .1
140 PRINT N .■ SQR< N >
150 NEXT N
160 END
100 REM CHAP 7, PROB 3
110 INPUT H
120 FOR X = 2 TO N STEP 2
130 PRINT X
140 NEXT X
150 END
A B C D A B C D A B C D A B C D A B C D
Since the Z and V loops are crossed, an error message will appear.
It reads and prints out five numbers rounded off to two places past
the decimal point.
1 0 0
REM CHAP 7,
PROB 11
110
GRAPHICS 8
120
COLOR 1
130
FOR K=1 TO
150 STEP
10
140
PLOT 0 .■ K : D R A H T 0 310,
K
150
NEXT K
160
FOR J=1 TO
310 STEP
10
170
PLOT J,0 : DRAWTO J, 15
0
180
NEXT J
Solutions to Odd-Numbered Problems
1 00
REM CH
hP 7,
PROP 13
110
INPUT
N
120
INPUT
X
130
LET L =
y
140
LET H =
y
150
LET S =
y
168
FOR 1 =
1 T 0 N
-1
170
INPUT
y
180
IF Y .>L
THEN
200
190
LET L =
y
2 0 0
IF X<H
THEN
■~« -~i rj
210
LET H =
y
220
LET S =
s+x
230
NEXT I
240
PRINT
"HIGHE
ST GRADE IS
250
PRINT
"LOWES
T GRADE IS
260
PRINT
" AUER A
GE IS " S-*"N
270
END
1 2 3
2 4 6
3 6 9
4 8 12
1 0 0
REM C
HAP 7, PROP 17
110
READ
N
120
FOR I
= 1 TO N
1 30
READ
M, R,D1,D2■D3,D4,D
I 40
PRINT
11 EMPLOYEE NUMBER
150
LET H
=D1 + D 2+D 3+D 4+D 5
160
IF H<
=40 THEN 180
1 70
LET P
=R*40+1.5'£R$< H-40
175
GOTO
1 ft Fi
180
LET P
= R $ H
185
PRINT
"PAY IS " P
188
NEXT
I
190
DATA
ET
2 0 0
DATA
2.4 ft . ft , 1 Li , ft . 7.1 ft
201
DAT A
5.. 3.75,7,8,8,6, 18
2 0 2
DATA
1,3.25,8,10,6,8,8
203
DATA
4.5.8.18. b, 10, f.
204
DATA
3,4.25,6,6,8,10,7
210
END
290 Hands-on BASIC
Chapter 8
1. 100 REM CHRP 8, PR OB 1
110 DIM XC 20 >
120 READ H
130 FOR 1=1 TO N
140 READ A
158 LET XCI>=A
160 NEXT I
170 FOR 1=1 TO N
180 PRINT XCI>
190 NEXT I
200 DATA 12
210 DATA 2, 1,4,3,2,4,5.. 6,3,5,4, 1
220 END
3. 100 REM CHAP 8, PROB 3
110 DIM AC 10. 10>
120 INPUT N
130 FOR R=1 TO N
140 FOR C=1 TO N
150 INPUT X
160 LET hC R.. C >=X
170 NEXT C
180 NEXT R
190 LET S=0
200 FOR 1=1 TO H
210 LET S=S+ACI, I >
220 NEXT I
230 PRINT "SUM OF MAIN DIAGONAL IS "
240 END
5. 100 REM CHAP 8, PROB 5
110 DIM AC 15, 15)
120 INPUT M,N
130 FOR R=1 TO M
140 FOR C=1 TO N
150 INPUT X
160 LET AC R,C>=X
170 NEXT C
180 NEXT R
190 LET S=0
Solutions to Odd-Numbered Problems
7.
9.
11 .
13.
15.
200 FOR R=1 TO M
210 FOR C=1 TO N
220 LET S = S +A<R. C >
230 NEXT C
240 NEXT R
250 PRINT "SUM OF ENTRIES
260 END
9 9999998
16
1 0 0
REM C
HAP 8,
PR OB
1 1
110
DIM X
< 1 0 0 }
120
INPUT
N
130
FOR I
= 1 TO
N
1 40
INPUT
A
150
LET X
< I >=A
160
NEXT
I
1 70
FOR I
= 1 TO
N
-1
180
IF X<
I + i > <
=
X< I
> THEN
190
LET T
=x<: i + i
2 0 0
LET X
<i + i >=
y
< I )
210
LET X
< I > = T
2 2 0
G 0 T 0
170
230
NEXT
I
240
FOR I
= 1 TO
N
250
PRINT
X< I
H
H .
260
NEXT
I
270
END
1 1
1 1 1
M M M
1
M
M M
0 0
{a h
Kl Kl Kl
1 1 1
IA !?4 M
Kl
1
Kl Kl
0 0
0 0
Kl Kl Kl
0 6 1
0 0 0
i
0
1 0 0
REM C
HAP 8,
PROB
15
110
DIM X
<2.5 >
120
FOR R
= 1 TO
230
291
17.
292 Hands-on BASIC
130 FOR C=1 TO 5
140 READ A
150 let x<r,c:j=a
160 NEXT C
170 NEXT R
180 DATA 2, 1,0.5.- 1
190 DATA 3 >2 > 1 > 3 > 1
2 0 0 F 0 R R = 1 T 0 2
210 FOR C=1 TO 5
220 PRINT H<R,C>,
230 NEXT C
240 PRINT
250 NEXT R
260 END
100 REM CHAP 8, PROB 17
110 DIM X< 20;20 >
120 INPUT M,N
130 FOR R=1 TO M
140 FOR C=1 TO N
150 INPUT A
160 LET X< R.. C J = A
170 NEXT C
180 NEXT R
190 FOR R=1 TO M
200 LET 8=0
210 FOR C=1 TO N
iliti LET S=S+X R j U )
230 NEXT C
240 PRINT "SUM OF ROW " R“ IS " S
250 NEXT R
260 FOR C=1 TO N
270 LET P=1
280 FOR R=1 TO M
290 LET P=P*X<R,C>
300 NEXT R
310 PR INT " PR0DUCT 0F C0LUMN " C; " IS " P
320 NEXT C
330 END
Solutions to Odd-Numbered Problems
100 REM CHAP 8, PROE! 19
110 DIM X(4,6 >
120 FOR R=1 TO 4
130 FOR C=1 TO 6
140 READ A
150 LET XCR,C:> = A
160 NEXT C
170 NEXT R
180 DAT A 48 .■ 40.73 .■ 1 20.100.. 90
1 90 DATA 75 .■ 130.. 90,1 40,1 1 0 85
200 DATA 50,72.. 1 40, 125.. 106,92
210 DATA 1 0 8.. 7 5 .■ 9 2.. 1 5 2 .■ 9 1 .■ 8 7
220 FOR C=1 TO 6
230 LET 8=0
240 FOR R=1 TO 4
2 5 U LET S=S+X < R .■ L-
260 NEXT R
270 PRINT "TOTAL-DAY “ id" IS " S
280 NEXT C
285 PRINT
290 FOR R=1 TO 4
300 LET 8=0
310 FOR C=1 TO 6
320 LET S=S + X<: R, C ;■
330 NEXT C
340 PRINT "TOTAL-SALESPERSON "j R;" IS
350 NEXT R
360 LET S — 0
370 FOR R=1 TO 4
380 FOR C =1 TO 6
390 LET 6 = S + X F!C
400 NEXT C
410 NEXT R
420 PRINT
430 PRINT "TOTAL SALES FOR THE WEEK IS "
440 END
100 REM CHAP 8, PROE: 21
1 1 0 D I M P ( 2 0 >.. X ( 2 0 >
120 PRINT "HOW LONG ARE THE ARRAYS "
130 INPUT N
294
Hands-on BASIC
140
FOR 1=1 TO
N
150
LET PC I>=I
160
NEXT I
170
FOR R=1 TO
N
180
INPUT A
190
LET XCR )=A
200
NEXT R
210
FOR 1=1 TO
N-l
220
if xcpc i >>:;
XC PC I +1 1
2 3 0
LET T=P<I >
240
LET PC I>=P<
I + 1 )
250
LET PC 1 + 1 >=
T
260
G 0 T 0 2 10
270
NEXT I
2 8 0
PRINT "P %'
11
2 9 0
PRINT
3 0 0
FOR 1=1 TO
N
310
PRINT PCI),
XC I
320
NEXT I
320
END
Chapter 9
1 0 0
REM CHAP 9,
PROE: 1
110
DIM A$C 50 }
120
INPUT A$
130
FOR 1=1 TO
LENC A$ >
140
PRINT ASCI,
I >
150
NEXT I
160
END
1 0 0
REM CHAP 9,
PROE: 3
110
DIM A$C 50 >
120
INPUT A$
130
LET A=8
140
LET E=0
150
LET 1=0
160
LET 0=0
170
LET U— @
180
FOR K= I TO
LENC A$)
190
IF A$CK,K>=
"A" THEN
THEN
A=A + i
Solutions to Odd-Numbered Problems
200 IF A$CK,K}="E" THEN E = E+1
210 IF ASC Kj K >=“ I" THEN 1 = 1 + 1
220 IF A$CkMO="0" THEN 0=0+1
230 IF ASC K, K ) = "U" THEN u=U +1
240 NEXT K
250 PRINT "A = "A
260 PRINT "E = "j E
270 PRINT "I = M
280 PRINT "O = "0
290 PRINT "U = "jU
300 END
100 REM CHAP 9, PROB 5
110 DIM ASC 50 >, BSC 50 >
120 INPUT AS
130 FOR 1=1 TO LENCAS)
140 IF ASC 1 1 I >=CHR$C 32 > THEN 160
1 50 LET B$< LENC B$ >+ 1 >=A$< I , I >
160 NEXT I
170 PRINT B$
180 END
100 REM CHAP 9, PROB 7
110 DIM A$< 50 >
120 LET C=0
130 FOR K =1 TO 5
140 INPUT AS
150 IF A$< 1 .■ 4 >< > " THE " THEN 170
160 LET C=C+1
170 FOR 1=2 TO LENC AS >-3
180 IF A$< I .. 1 + 3 X > " THE " THEN 200
190 LET C=C+1
200 NEXT I
210 NEXT K
220 PRINT C
230 END
100 REM CHAP 9, PROB 9
110 DIM A SC 50 >
120 INPUT AS
130 LET C = 0
296 Hands-on BASIC
140 FOR K=1 TO LEN< A$ >-1
150 IF A$< K, K+1 X >" IN" THEN 170
160 LET C=C+1
170 NEXT K
180 PRINT C
190 END
Chapter 10
1. 100 FOR K = 1 TO
110 READ PITCH.. LENGTH
120
FOR L
= 1
TO
LENGTH
130
SOUND
0 ,
PITCH
, 10,8
—
140
NEXT
L
150
NEXT
K
160
DATA
121
, 40
, 0
, 1 0 , 1 08,40 , 0 , 1 0
170
DATA
96..
40,
0 ,
10.. 121,40 0 , 1 0
180
DATA
121
, 40
, 0
, 1 0 , 1 08,40,0 .. 1 0
190
DATA
96.*
40,
0 ,
10.. 121,40,0, 10
2 0 0
DATA
96 ,
40,
0 ,
10,91,4 0,0 , 1 0
210
DATA
81,
40,
0 ,
50
220
DATA
96 .*
40,
0 ,
10,91,4 0,0, 10
230
DATA
81,
40,
0 ,
50
240
DATA
81,
20,
0 ,
5,72*20,0.5
—
250
DATA
81,
20,
0 ,
5,91,20,0,5
260
DATA
96..
40,
0 ,
5, 121,20,0,2 0
270
DATA
81,
20,
0 ,
5,72.20.0.5
2 8 0
DATA
81,
2 0,
0 ,
5,91,2 0,0,5
290
DATA
96..
40,
0 ,
5,121,20,0,20
■ _
300
DATA
121
, 40
, 0
, 10, 162,40,0, 10
310
DATA
121
, 40
, 0
, 50
—
320
DATA
121
, 40
, 0
, 10,162,4 0,0, 1 0
330
DATA
121
, 40
, 0
, 50
340 END
3. 55
15
36
5. 500 REM SUBROUTINE
510 LET L=X< 2 >
Solutions to Odd-Numbered Problems 297
520
FOR 1=3 TO
X<1>+l
530
IF L>=X<I>
THEN 550
540
LET L = X<I>
550
NEXT I
5 6 0
RETURN
900
REM SUBROUTINE
910
LET S1—8
920
LET 82=0
930
FOR 1=2 TO
YC 1 > +1
940
LET S1= S1+ Y
( I >
950
LET S2=S2+Y
< I > A 2
960
NEXT I
970
LET M=S1/Y<
1 >
9 8 0
LET S=SQR<C
Y<1 )*S2-S1
<. Y < 1 ')%(. Y k 1 )
-1 > > >
990
RETURN
Chapter 11
1 0 0
REM CHAP 11
, PROB 1
110
FOR 1=1 TO
■“« cr
J
120 LET N = IN T < 10 0 * R N D < 1 > > /10
130 PRINT H,
140 NEXT I
150 END
3. A typical output is:
0.15
0.18
0.14
0.19
0.14
0 .:
0.02
0.0?
0.12
0.06
0.13
0.0 1
0.09
0.1 3
0.0!
5. 90 REM CHAP 11, PROP 5
1 0 0 F U R! 1 = 1 T U 5
110 READ N
120 LET H=0
130 LET T=0
140 FOR J=i TO N
150 LET X=INT<2 1 RND<0 )+l>
160 IF X=1 THEN 190
298 Hands-on BASIC
170 LET T=T+1
180 GOTO 200
190 LET H = H+1
200 NEXT J
210 PRINT
220 PRINT "FOR ";Ni" TOSSES THERE WERE"
230 PRINT H.;” HEADS AND " ;T;" TAILS"
240 NEXT I
250 DATA 1 0 .■ 5 0 , 1 0 0 , 5 0 0 .. 1 0 0 0
260 END
7. 90 REM CHAP 11, PROB 7
100 LET S=0
110 FOR 1=1 TO 100
120 LET S=S+RND<0>
130 NEXT I
140 PRINT S/100
150 END
9. 90 REM CHAP 11, PROB 9
100 LET M=0
110 FOR 1 = 1 T 0 10 0 0
120 LET A=60*RND<0>
130 LET B=60*RND<0>
140 IF ABS< A-B >>10 THEN 160
150 LET M=M+1
160 NEXT I
170 PRINT "PROBABILITY OF A MEET IS ";M/1000
180 END
11. 90 REM CHAP 11, PROB 11
100 FOR 1=1 TO 25
110 LET S=0
120 FOR J=1 TO 12
130 LET S=S+RNDC0>
140 NEXT J
158 LET R = 10+2-t:< S - 6 >
160 PR I NT INT<100TR+.5 >/100,
170 NEXT I
180 END
Solutions to Odd-Numbered Problems 299
Chapter 12
1. A possible record structure would be
Variable Description
as follows.
Approximate Length
TITLES
Title of cassette
30
LABELS
Record company
20
NAMES
Name of musicians
50
KINDS
Category of music
15
PRICE
Price of cassette
5
3. A possible record structure would be
Variable Description
as follows.
Approximate Length
NAMES
Name of item
50
ROOMS
Location of item
15
AMT
Value of item
10
5. A program for entering a month's charges and totalling them for a
particular credit card follows.
1 0 0
REM C
HAP 12,
F'ROE: 5
110
DIM C
ARDS': 20
>, NAMESC 30 >, TEMPS
«:' 30 )
120
DIM D
ATESC 10
;■, DES$< 50 >, ANS$< 3
130
PRINT
"ARE Y
QIJ CREATING THE
FILE"
140
PRINT
"FOR THE FIRST TIME? <
Y
150
INPUT
ANSS
160
IF AN
S$< > " V "
THEN 190
1 70
OPEN
#1,8,0,
"D = CARD.DAT"
180
G 0 T 0
240
190
PRINT
"DO YC
U WISH TO OBTAIN
CREDIT"
0 0
PRINT
"CARD
TOTALS ONLY? "j
210
INPUT
ANSS
220
IF AN
C.0
II
THEN 420
2 3 0
OPEN
#1,9,0,
"D:CARD.DAT"
240
PRINT
"NAME
OF CARD : "i
250
INPUT
CARDS
300 Hands-on BASIC
269
IF CARD$= " QUIT"
THEN 410
270
PRINT
#1 CARDS
2 8 0
PRINT
"NAME OF
STORE : "
290
INPUT
NAMES
3 0 0
PRINT
#1; NAMES
310
PRINT
"DATE OF
PURCHASE : "
320
INPUT
DATES
330
PRINT
#1DATES
340
PRINT
"DESCRIPTION OF PURC
350
INPUT
DESS
360
PRINT
#1 i DESS
370
PRINT
"COST OF
PURCHASE = "
3 8 0
INPUT
AMT
390
PRINT
#1AMT
4 0 0
GOTO ;
240
410 CLOSE #1
420 OPEN #1,4,0,"D=CARD.DAT"
430 REM SUM THE CHARGES
440 LET SUM=0
450 PRINT "NAME OF CARD TO TOTAL= "
460 INPUT TEMPS
470 IF TEMP$="QUIT" THEN END
480 TRAP 540
490 INPUT #1CARDS, NAMES, DATES
500 INPUT #1; DESS, AMT
510 IF CARD$< >TEMP$THEN 490
520 LET SUM = SUM + AMT
530 G0TO 490
540 PRINT "TOTAL FOR "i TEMPS;" IS ">SUM
550 CLOSE #1
560 G0TO 420
Note: This program does not accumulate the information on the file.
You might want to provide for adding information to the file as was
done in Program Example 2.
INDEX
ABS 139,146
Animation 47-48,53
Arithmetic in BASIC 11-14,58,66
Arithmetic priority 66,67
Array Operations program 180
Arrays 162
ASC 199,202
ATASCII character set 202
Automobile License Fees program 116
Averaging Numbers program 121
BASIC arithmetic 11-14,58,66
BASIC functions
ABS 139,144
ASC 199,202
CHR$ 198,202
INT 138,144,145
LEN 194,199,201
RND 236-241
SGN 139,144,145
SQR 137,144-145
BASIC origins 6
BASIC parentheses 67
BASIC graphics statements 40-46,
49,50-52
BASIC programs
entering and controlling 32
execution 23,65,71
retrieval 64,70
storage 63,70
BASIC program requirements 30
line numbers 30
order 30
spacing 31
BASIC language cartridge 2,11,16
BASIC statements
CONT 27,33
COLOR 40,49,54
CLOSE 252,256
DATA 79-80,87
DIM 164,165,172,252
DOS 62
DRAWTO 41-46,50-52
END 22,257
FOR NEXT 132-137,140-144
GET 109
GOSUB 212-215,217-219
GOTO 25,26,112
GRAPHICS 40,49
IF THEN 104,113
INPUT 25,28,46,76,86,252
LET 22,30,35,86
OPEN 252,256
PLOT 40,50-52
PRINT 11,17,22,81,85,252
READ 78,80,86
REM 82,89
RETURN 212-215,217-219
SETCOLOR 50,54
STEP 132
TRAP 254,258
BASIC variables, names 33-35
Birthday Pairs in a Crowd program
246
Bringing up ATARI BASIC 16
Carpet Estimating program 222
Catenation 199-200,203
Character strings 34,192,193,
201-203
CHR$ 198,202
CLEAR key 13
302 Index
Clear screen 13
CLOSE 252,256
COLOR 40,49,54
Commands
LIST 22,28,32
LOAD 64
NEW 24
RUN 23,65,71
SAVE 63,70
Conditional transfer 105-110,113
Converting Temperature program 92
Correcting mistakes 13,18,30
Course Grades program 177
Crossed loops 136,143
Cursor 11
DATA 79-80,87
Deleting lines in a BASIC program 23
Depreciation Schedule program 150
Designing a House program 227
DIM 164,165,172,252
Direct mode 9,16
Discovery method 5-6
Disk Drive 62,69
Disk file 63
Distortion 216
Distribution of Random Numbers
program 244
DOS diskette 62,69
DOS Manual 2,70
DRAWTO 41-46,50-52
Editing 13,18,30
END 22,257
End of file 254
E Notation 61-62,68-69
Entering graphics mode 40,49
Error correction 13,18,30
Error messages 13,18
Exact Division program 149
Examination Grades program 174
Exponentiation 59-60
Finding the Average of a Group
Numbers program 147
Flipping Coins program 242
Formatting a diskette 62,69-70
FOR NEXT 132-137,140-144
Function
ABS 139,144
INT 138,144,145
RND 236-241
SGN 139,144,145
SQR 137,144-145
GET 109
GOSUB 212-215,217-219
GOTO 25,26,112
GRAPHICS 40
Graphics mode 40,49,50
IF THEN 104,113
INPUT 25,28,46,76,86,252
Input/Output Control Block 256
INT 138,144,145
Interrupting program executions 27,32
Interrupting INPUT loops 26,32
Inverse key 10
IOCB 256,257
Jumping out of loops 27,32
Jumping out of INPUT loops 26,33
Keyboard 10
Keys
BREAK 10,26,32
CLEAR 22
CONTROL 13,18,30
CTRL 13,18,30
DELETE BACK S 18
DELETE BACK SPACE 18
INSERT 18
RESET 16
RETURN 11,16,18
SHIFT 10,18
SYSTEM RESET 16
13
13
T 30
Index 303
LEN 194,199,201
LET 22,30,35,86
Line deletion 23
LIST 22,28,32
LOAD 64,70
Loops, crossed 136,143
Loops, FOR NEXT 132-137,140-144
Loops, INPUT 33
Loudness 211
Mail List Data Entry program 259
Mailing Label program 260
Matrix 162
Mean 232,241
Menu-Driven Mailing program 264
Modifying the MAIL.DAT file
program 261
NEW 24
Numeric variable definition 34
ON/GOSUB 219
OPEN 252,256
Parentheses 67-68
Pitch 210
PLOT 40,50-52
PRINT 11,17,22,81,85,252
Printout of Number Patterns program
115
Priority of operations 66-68
Programs in book
Array Operations 180
Automobile License Fees 116
Averaging Numbers 121
Birthday Pairs in a Crowd 246
Carpet Estimating 222
Converting Temperature 92
Course Grades 177
Depreciation Schedule 150
Designing a House 227
Distribution of Random
Numbers 244
Exact Division 149
Examination Grades 174
Finding the Average of a Group
of Numbers 147
Flipping Coins 242
Mail List Data Entry program 259
Mailing Label program 260
Menu-Driven Mailing program 264
Modifying the MAIL.DAT file
program 261
Printout of Number Patterns 115
Random Integers 243
Random Walk 245
Replacement Code 204
Rounding Off Dollar Values
to Cents 220
Selected Labels program 261
String Reversal 203
Sum and Product of Numbers 93
Tempature Conversion Table 148
Unit Prices 90
Word Count 204
Writing a Song 219
Random Integers program 243
Random file 258
Random numbers 236,240
Random Walk program 245
READ 78,80,86
Relational Operators 104-106,113,197
REM 82,89
Replacement Code program 204
Reserve words 35
RETURN 212-215,217-219
Retrieving BASIC programs 64,70
Reverse Video 10
RND 236-241
Rounding Off Dollar Values to Cents
program 220
RUN 23,65,71
SAVE 63,70
Screen editing 13,18,30
Selected Labels program 261
Sequential file 258
SETCOLOR 50,54
SGN 139,144,145
SOUND 209-212,216
304 Index
Spacing of printout 85,88
Split screen 51
SQR 137,144-145
Standard deviation 234,241
STEP 132,140-141
Storing BASIC programs 63,70
String output 87,192
String Reversal program 203
String variable definition 34
Subscripts 162-163,170-172
Subroutines 212,217-219
Substrings 195-196,202
Sum and Product of Numbers
program 93
System Master Diskette 62
System restart 16
Temperature Conversion Table
program 148
Text mode 41,50,51
Tracing programs 110-111
Transfer
conditional 105-110,113
unconditional 25,112
TRAP 254,258
Troubleshooting programs 110-111
Turning on/off your computer
10,16,62
Unconditional transfer 25,112
Unit Prices program 90
Variable names 17,33,34
Variables, subscripted 162,163,
170-172
Voice 210
Word Count program 204
Writing a Song program 219
<- 13
-► 13
t 30
CTRL
13,18,30
RETURN! 11,16
< RETURN > 22
+ 11,12,58
- 11,14,58
/ 11,12,58
* 11,13,58
= 14
~ 59-60
■ 11,13
CONT Restarts execution after use of the BREAK key
DOS Places the computer in a mode for certain disk
operations
LIST Displays the program in memory
LIST lists entire program
LIST 40,310 lists lines 40 through 310
LOAD filename Brings the specified program from
diskette into memory
LOAD “D:MENU"
NEW Erases the contents in memory
RUN Executes the program
SAVE filename Puts the specified program in
memory out to diskette
SAVE: “D: LABELS”
STRING FUNCTIONS
ASC(string) Returns ASCII code of first character of
specified string
LET A = ASCCBS)
CHR$ (number) Takes an ASCII code number and
returns the corresponding character
LET P$ = CHR$(65)
LEN(string) Returns the length of a string
FOR X = 1 TO LEN(A$)
STR$ (number) Returns the string representation of
a number
LET A$ = STR$(27)
VAL(string) Converts a string of digits into a number
LET P = VAL(A$)
v$(nl,n2) Returns a substring of v$ starting with
character nl and running through character n2:
(not a proper function but included here because it
is an important implied function)
IF N$(1,4) = “NAME” THEN 300
NUMERIC FUNCTIONS
ABS(number) Computes absolute value
LET X = ABS(-7)
INT(number) Returns the greatest integer less than
or equal to the specified number
LET Y = INTC2.7) LET D - INT(RND(0)* 1001
RND(0) Returns a random number between (and
including) 0 up to (but not including) 1
LET D = 1 + RND(0}*9
SGN(number) Returns the sign of the specified
numeric expression
LET P = SGN(R - E)
SQR(number) Returns the square root of a number
LETC = SQR(A*A + B*B)
GRAPHICS AND SOUND STATEMENTS
COLOR n Chooses the color register to be used in
color graphics
COLOR 1
DRAWTO x,y Draws a line from the current
position of the graphics pen to the point specified
DRAWTO 10,15
GRAPHICS n Specifies which of the 8 graphics
modes are to be used
GRAPHICS 8
PLOT x,y Causes one point to be plotted at the point
specified
PLOT X,Y PLOT 5,17
SETCOLOR register#,hue,brightness Stores hue
and brightness data in specified color register
SETCOLOR 2,6,4
SOUND nl,n2,n3,n4 Controls which of 4 voices,
sound pitch, distortion, and volume of a note
SOUND 2,121,10,10.8
QUICK REFERENCE GUIDE
STATEMENTS
*
CLOSE #n Closes the specified open file
CLOSE #1
DATA datalist Contains values to be assigned to
variables in a READ statement
DATA 7.2,BOY.3,4.5
DIM v(n) Reserves space for arrays and strings
DIM A(10,20),B$(50)
END Stops program execution; closes files; turns off
sound
FOR. .TO/NEXT Creates a loop
FOR J = 1 TO 10 FOR A = 2*X TO Y STEP 2
NEXT J NEXT A
GOSUB line# Calls a subroutine beginning at
specified line number
GOSUB 500
GOTO line# Jumps to specified line number
(unconditional jump)
GOTO 412
IF condition THEN line# Jumps to the line number
specified after THEN when the condition is true
(conditional jump)
IF X> 10 THEN 320
IF condition THEN statement Performs the state¬
ment after THEN when the condition is true
IF Y-2 = 7 THEN END
INPUT v Causes program execution to pause for
input from keyboard
INPUT A, B INPUT D$
INPUT#n;v Causes information to be read from a
file on diskette
INPUT #1 ;A,G$
LET v = expression Assigns a value to a variable
LET X = 7 LET C = C +1
ON v GOSUB nl,n2,.. Causes a jump to one of
several subroutines depending on the value of the
variable after the ON
ON N GOSUB 300,350,400
ON v GOTO nl,n2,.. Causes a jump to one of
several line numbers depending on the value of the
variable after ON
ON N GOTO 100,200.252
OPEN #nl,n2,n3, filename Opens a file for input or
output operations; nl, n2, and n3 stand respectively
for the IOCB number, I/O mode, and rotated print¬
ing control (nearly always set to 0)
OPEN# 1,4,0,"D:DATA"
PRINT list Causes output to be placed on the
specified output device; default is the screen
PRINT A,B PRINT C$.X(J)
PRINT #1 ;A$
READ variable list Reads the next item in the DATA
list and assigns it to a specified variable
READ B$,NUMBER,M
REM Allows insertion of a comment in a
program line
REM SUBROUTINE SCALE
RESTORE Resets data in DATA statements so it can
be read again
RESTORE restores all DATA statements
RESTORE 90 restores data in statement 90
RETURN Returns program control from a subrou¬
tine to the line following the GOSUB that called it
TRAP line# Jumps to specified line number if an
INPUT error occurs
TRAP 790
SPECIAL KEYS
[3I3EG3 Move cursor
| BACKSPACE | Moves cursor one space to left,
deleting whatever was there and
leaving a space
| BREAK] Interrupts anything in progress and
returns to command level
| CLEAR"] Clears the screen
|CTRL|
| DELETE|
Deletes the character under
he cursor and contracts the line
|ctrl|
| INSERT |
Inserts a space
| RETURN^ Signifies end of current line; when
editing, accepts edit changes that
were made in the line.
IMPORTANT ERROR MESSAGES
ERROR
CODE PROBLEM
2 Out of Memory: Insufficient room for statement or variable
3 Wrong Value: A negative value used where a positive one
is required or value is not within allowed range
5 String Too Long: Attempt to store beyond the
DIMensioned string length
6 Out of Data: READ statement requires more data than
supplied by the DATA statement(s)
7 Integer out of range: Value is not the required positive
integer or is >32767
8 INPUT Type Conflict: Attempt to INPUT a nonnumeric
value into a numeric variable
9 DIM Error: Subscript out or range; reference to an
unDIMensioned variable; attempt to reDIMension a variable;
or DIM value is >32767
11 Overflow/Underflow: Attempt to divide by zero or
reference to a number >1E98 or <1E -99
12 Line Not Found: Number after GOTO, GOSUB, or THEN
does not match any line number
13 NEXT Without FOR or improperly nested FOR/NEXT
statements
14 Line Too Long: Statement is too long or too complex
16 RETURN Without GOSUB
18 Invalid String Characters or string in VAL function
is not a numeric string
19 Program Too Long for LOAD
20 Bad Device Number: Device number not in the required
range of 1 through 7
128 BREAK Abort: User pressed the BREAK key during an
I/O operation
129 IOCB Already Open: IOCB already in use for another file
or device
130 Nonexistent Device: Specified a filename without a device
(i.e. "MYFILE" instead of "D:MYFILE")
131 IOCB Write Only: READ command to a write-only device
133 Device or File Not Open: No OPEN specified for the device
134 Bad IOCB Number: IOCB number is not in the required
range of 1 through 7
135 IOCB Read Only: Attempt to write to a read-only device
or file
136 EOF: End of file has been reached
138 Device Timeout: Device does not respond
141 Cursor Out of Range: Cursor out of the allowed range
for the graphics mode
144 Protected Diskette: Attempt to write on a write-protected
diskette
147 RAM Insufficient: Insufficient RAM for operating selected
graphics mode
160 Drive Number Error: Drive number is out of the allowed
1 through 8 range or computer was switched on before
the drive was switched on
162 Disk Full
163 Unrecoverable System Data I/O Error: Diskette or DOS
may be bad
164 File Number Mismatch: Problems with links on the disk
(try turning the system off and on again)
165 Filename Error: Filename includes illegal characters
169 Directory Full: Not enough room on diskette
170 File Not Found: File does not exist on diskette
*IOCB = Input/Output Control Block (IOCB number
corresponds to the device number)
About the Author
HERBERT PECKHAM is a principal in Computer Literacy
a firm specializing in materials for computer educa¬
tion. He formerly was professor of mathematics and
physics at Gavilan College where he also taught
courses in computing languages.
The author has served on the Executive Board of the
American association of Physics Teachers and was
a member of that organization's committee on com¬
puters in physics teaching. Professor Peckham is
author and co-author of numerous books and mono¬
graphs on BASIC, Pascal, and computer applications.
When using, fold flap
inside back cover.
Hands-On
BASIC
FOR THE ATARI® 400/800/1200XL
J
w
o
J
ISBN □ — 07 — □4 C H C 14 — 1
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